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  • Data adapter not filling my dataset

    - by Doug Ancil
    I have the following code: Imports System.Data.SqlClient Public Class Main Protected WithEvents DataGridView1 As DataGridView Dim instForm2 As New Exceptions Private Sub Button1_Click_1(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles startpayrollButton.Click Dim ssql As String = "select MAX(payrolldate) AS [payrolldate], " & _ "dateadd(dd, ((datediff(dd, '17530107', MAX(payrolldate))/7)*7)+7, '17530107') AS [Sunday]" & _ "from dbo.payroll" & _ " where payrollran = 'no'" Dim oCmd As System.Data.SqlClient.SqlCommand Dim oDr As System.Data.SqlClient.SqlDataReader oCmd = New System.Data.SqlClient.SqlCommand Try With oCmd .Connection = New System.Data.SqlClient.SqlConnection("Initial Catalog=mdr;Data Source=xxxxx;uid=xxxxx;password=xxxxx") .Connection.Open() .CommandType = CommandType.Text .CommandText = ssql oDr = .ExecuteReader() End With If oDr.Read Then payperiodstartdate = oDr.GetDateTime(1) payperiodenddate = payperiodstartdate.AddSeconds(604799) Dim ButtonDialogResult As DialogResult ButtonDialogResult = MessageBox.Show(" The Next Payroll Start Date is: " & payperiodstartdate.ToString() & System.Environment.NewLine & " Through End Date: " & payperiodenddate.ToString()) If ButtonDialogResult = Windows.Forms.DialogResult.OK Then exceptionsButton.Enabled = True startpayrollButton.Enabled = False End If End If oDr.Close() oCmd.Connection.Close() Catch ex As Exception MessageBox.Show(ex.Message) oCmd.Connection.Close() End Try End Sub Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles exceptionsButton.Click Dim connection As System.Data.SqlClient.SqlConnection Dim adapter As System.Data.SqlClient.SqlDataAdapter = New System.Data.SqlClient.SqlDataAdapter Dim connectionString As String = "Initial Catalog=mdr;Data Source=xxxxx;uid=xxxxx;password=xxxxx" Dim ds As New DataSet Dim _sql As String = "SELECT [Exceptions].Employeenumber,[Exceptions].exceptiondate, [Exceptions].starttime, [exceptions].endtime, [Exceptions].code, datediff(minute, starttime, endtime) as duration INTO scratchpad3" & _ " FROM Employees INNER JOIN Exceptions ON [Exceptions].EmployeeNumber = [Exceptions].Employeenumber" & _ " where [Exceptions].exceptiondate between @payperiodstartdate and @payperiodenddate" & _ " GROUP BY [Exceptions].Employeenumber, [Exceptions].Exceptiondate, [Exceptions].starttime, [exceptions].endtime," & _ " [Exceptions].code, [Exceptions].exceptiondate" connection = New SqlConnection(connectionString) connection.Open() Dim _CMD As SqlCommand = New SqlCommand(_sql, connection) _CMD.Parameters.AddWithValue("@payperiodstartdate", payperiodstartdate) _CMD.Parameters.AddWithValue("@payperiodenddate", payperiodenddate) adapter.SelectCommand = _CMD Try adapter.Fill(ds) If ds Is Nothing OrElse ds.Tables.Count = 0 OrElse ds.Tables(0).Rows.Count = 0 Then 'it's empty MessageBox.Show("There was no data for this time period. Press Ok to continue", "No Data") connection.Close() Exceptions.saveButton.Enabled = False Exceptions.Hide() Else connection.Close() End If Catch ex As Exception MessageBox.Show(ex.ToString) connection.Close() End Try Exceptions.Show() End Sub Private Sub payrollButton_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles payrollButton.Click Payrollfinal.Show() End Sub End Class and when I run my program and press this button Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles exceptionsButton.Click I have my date range within a time that I know that my dataset should produce a result, but when I put a line break in my code here: adapter.Fill(ds) and look at it in debug, I show a table value of 0. If I run the same query that I have to produce these results in sql analyser, I see 1 result. Can someone see why my query on my form produces a different result than the sql analyser does? Also here is my schema for my two tables: Exceptions employeenumber varchar no 50 yes no no SQL_Latin1_General_CP1_CI_AS exceptiondate datetime no 8 yes (n/a) (n/a) NULL starttime datetime no 8 yes (n/a) (n/a) NULL endtime datetime no 8 yes (n/a) (n/a) NULL duration varchar no 50 yes no no SQL_Latin1_General_CP1_CI_AS code varchar no 50 yes no no SQL_Latin1_General_CP1_CI_AS approvedby varchar no 50 yes no no SQL_Latin1_General_CP1_CI_AS approved varchar no 50 yes no no SQL_Latin1_General_CP1_CI_AS time timestamp no 8 yes (n/a) (n/a) NULL employees employeenumber varchar no 50 no no no SQL_Latin1_General_CP1_CI_AS name varchar no 50 no no no SQL_Latin1_General_CP1_CI_AS initials varchar no 50 no no no SQL_Latin1_General_CP1_CI_AS loginname1 varchar no 50 yes no no SQL_Latin1_General_CP1_CI_AS

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  • Synchronizing an ERWin model with a Visual Studio 2008 GDR 2/2010 db project

    - by Grant Back
    I am looking for options to get our vast collection of DB objects across many DBs into source control (TFS 2010). Once we succeed here, we will work toward generating our alter scripts for a particular DB change via TFS build. The problem is, our data architecture group is responsible for maintaining the DB objects (excluding SPs), and they work within a model centric process, via ERWin. What this means, is that they maintain the DBs via ERWin models, and generate alters from them that are used to release changes. In order to achieve our goal of getting the DB objects (not just the ERWin models) into TFS, I believe the best option is to do this via Visual Studio DB projects. From what I can tell, there is very little urgency for CA to continue supporting an integration between ERWin and Visual Studio, that no longer works as of Visual Studio 2008 DB Ed. GDR. If I have been mislead in this regard, please feel free to set me straight. One potential solution is to: Perform changes in the ERWin model. Take the alter script generated from ERWin, and import the script into the appropriate Visual Studio DB project, updating the objects in the in the DB project Check the changed objects in the DB project into TFS. TFS Build executes to generate the alter scripts that will be used to push the changes through our release process. My question is, is this solution viable, or are there any other options?

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  • Mocking with Boost::Test

    - by Billy ONeal
    Hello everyone :) I'm using the Boost::Test library for unit testing, and I've in general been hacking up my own mocking solutions that look something like this: //In header for clients struct RealFindFirstFile { static HANDLE FindFirst(LPCWSTR lpFileName, LPWIN32_FIND_DATAW lpFindFileData) { return FindFirstFile(lpFileName, lpFindFileData); }; }; template <typename FirstFile_T = RealFindFirstFile> class DirectoryIterator { //.. Implementation } //In unit tests (cpp) #define THE_ANSWER_TO_LIFE_THE_UNIVERSE_AND_EVERYTHING 42 struct FakeFindFirstFile { static HANDLE FindFirst(LPCWSTR lpFileName, LPWIN32_FIND_DATAW lpFindFileData) { return THE_ANSWER_TO_LIFE_THE_UNIVERSE_AND_EVERYTHING; }; }; BOOST_AUTO_TEST_CASE( MyTest ) { DirectoryIterator<FakeFindFirstFile> LookMaImMocked; //Test } I've grown frustrated with this because it requires that I implement almost everything as a template, and it is a lot of boilerplate code to achieve what I'm looking for. Is there a good method of mocking up code using Boost::Test over my Ad-hoc method? I've seen several people recommend Google Mock, but it requires a lot of ugly hacks if your functions are not virtual, which I would like to avoid. Oh: One last thing. I don't need assertions that a particular piece of code was called. I simply need to be able to inject data that would normally be returned by Windows API functions.

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  • Is Form validation and Business validation too much?

    - by Robert Cabri
    I've got this question about form validation and business validation. I see a lot of frameworks that use some sort of form validation library. You submit some values and the library validates the values from the form. If not ok it will show some errors on you screen. If all goes to plan the values will be set into domain objects. Here the values will be or, better said, should validated (again). Most likely the same validation in the validation library. I know 2 PHP frameworks having this kind of construction Zend/Kohana. When I look at programming and some principles like Don't Repeat Yourself (DRY) and single responsibility principle (SRP) this isn't a good way. As you can see it validates twice. Why not create domain objects that do the actual validation. Example: Form with username and email form is submitted. Values of the username field and the email field will be populated in 2 different Domain objects: Username and Email class Username {} class Email {} These objects validate their data and if not valid throw an exception. Do you agree? What do you think about this aproach? Is there a better way to implement validations? I'm confused about a lot of frameworks/developers handling this stuff. Are they all wrong or am I missing a point? Edit: I know there should also be client side kind of validation. This is a different ballgame in my Opinion. If You have some comments on this and a way to deal with this kind of stuff, please provide.

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  • What is the best practice in regards to building composite dtos off of an aggregate root with domain

    - by Chance
    I'm trying to figure out the best approach/practice for assembling a composite data transfer object off of an aggregate root and would love to hear people's thoughts on this. For example, lets say I have a root that has a few domain objects as children. I want to assemble a specific view dto, based on some business logic, that either has attributes or full dto's of it's objects. What I'm struggling with is trying to figure out where that assembly should happen. I can see it going on the domain object of the aggregate root as there is some business logic associated with it. The benefits of this approach from what I've deduced thus far is that it should reduce the inevitable business logic from bleeding outisde of the domain object. It also allows for private methods that take care of tasks that could become more complex from an external builder. The downsides being that the domain object becomes much more entrenched in the application's workflow and represents much more than just the domain object. It also could become very large in the scenario where you need multiple composite Dtos. Alternatively, I could also see it belonging to some form of transfer object assembler where there is a builder for each domain object. The domain objects would still be responsible for GetDto() and UpdateFromDto(dto). Outside of that, the builder would handle the construction and deconstruction of composite dtos. The downside is kind of mentioned above, where I fear this will easily lead to developers unfamiliar with DDD bleeding a ton of business logic into the assembler which is what I want to desperately avoid. Any thoughts would be greatly apperciated.

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  • Pagination in a Rich Domain Model

    - by user246790
    I use rich domain model in my app. The basic ideas were taken there. For example I have User and Comment entities. They are defined as following: <?php class Model_User extends Model_Abstract { public function getComments() { /** * @var Model_Mapper_Db_Comment */ $mapper = $this->getMapper(); $commentsBlob = $mapper->getUserComments($this->getId()); return new Model_Collection_Comments($commentsBlob); } } class Model_Mapper_Db_Comment extends Model_Mapper_Db_Abstract { const TABLE_NAME = 'comments'; protected $_mapperTableName = self::TABLE_NAME; public function getUserComments($user_id) { $commentsBlob = $this->_getTable()->fetchAllByUserId((int)$user_id); return $commentsBlob->toArray(); } } class Model_Comment extends Model_Abstract { } ?> Mapper's getUserComments function simply returns something like: return $this->getTable->fetchAllByUserId($user_id) which is array. fetchAllByUserId accepts $count and $offset params, but I don't know to pass them from my Controller to this function through model without rewriting all the model code. So the question is how can I organize pagination through model data (getComments). Is there a "beatiful" method to get comments from 5 to 10, not all, as getComments returns by default.

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  • Why represent shopping carts and order invoices differently in a domain model?

    - by Todd
    I've built some shopping cart systems in the past, but I always designed them such that the final order invoice is just a shopping cart that has been marked as "purchased". All the logic for adding/removing/changing items in a cart is also the logic for the order. All data is stored in the same tables in the database. But it seems this is not the proper way to design an e-commerce site.. Can someone explain the benefit of separating the shopping cart from invoices in the domain model? It seems to me this would lead to a lot of duplicated code, an extra set of tables in the database, and make it harder to maintain in the event the system need to start accommodating more complicated orders (like specifying selected options for an item which may or may not change the price/availability/shipping time of the order). I'm assuming I just haven't seen the light, as every book and other example I see seems to separate these two seemingly similar concerns -- but I can't find any explanation as to the benefit of doing such! It's also the case in the systems that I design that changes are often made after the initial order is confirmed. It's not uncommon for items to be removed, replaced, or added afterwards (but prior to fulfillment).

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  • Parallelizing L2S Entity Retrieval

    - by MarkB
    Assuming a typical domain entity approach with SQL Server and a dbml/L2S DAL with a logic layer on top of that: In situations where lazy loading is not an option, I have settled on a convention where getting a list of entities does not also get each item's child entities (no loading), but getting a single entity does (eager loading). Since getting a single entity also gets children, it causes a cascading effect in which each child then gets its children too. This sounds bad, but as long as the model is not too deep, I usually don't see performance problems that outweigh the benefits of the ease of use. So if I want to get a list in which each of the items is fully hydrated with children, I combine the GetList and GetItem methods. So I'll get a list and then loop through it getting each item with the full cascade. Even this is generally acceptable in many of the projects I've worked on - but I have recently encountered situations with larger models and/or more data in which it needs to be more efficient. I've found that partitioning the loop and executing it on multiple threads yields excellent results. In my first experiment with a list of 50 items from one particular project, I did 5 threads of 10 items each and got a 3X improvement in time. Of course, the mileage will vary depending on the project but all else being equal this is clearly a big opportunity. However, before I go further, I was wondering what others have done that have already been through this. What are some good approaches to parallelizing this type of thing?

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  • ExtJs store, how to load data using a MemoryProxy

    - by Miau
    Hi there I m trying to load a json store using a MemoryProxy ( i need to use a proxy because I use different sources depending on scenarios) it kinda looks like this var data = Ext.decode(gridArrayData); var proxy = new Ext.data.MemoryProxy(data); var store = new Ext.data.GroupingStore({ proxy: proxy }); however when I inspect this I can see that the proxy has 10 rows of data, but not the store I m lost as to why Any pointers?

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  • JQuery getJSON Callback Returning Null Data

    - by user338828
    I have a getJSON call that is called back correctly, but the data variable is null. The python code posted below is executed by the getJSON call to the demandURL. Any ideas? javascript: var demandURL = "/demand/washington/"; $.getJSON(demandURL, function(data) { console.log(data); }); python: data = {"demand_count":"one"} json = simplejson.dumps(data) return HttpResponse(json, mimetype="application/json")

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  • Oracle sample data problems

    - by Jay
    So, I have this java based data trasformation / masking tool, which I wanted to test out on Oracle 10g. The good part with Oracle 10g is that you get a load of sample schemas with half a million records in some. The schemas are : SH, OE, HR, IX and etc. So, I installed 10g, found out that the installation scripts are under ORACLE_HOME/demo/scripts. I customized these scripts a bit to run in batch mode. That solves one half of my requirement - to create source data for my testing my data transformation software. The second half of the requirement is that I create the same schemas under different names (TR_HR, TR_OE and so on...) without any data. These schemas would represent my target schemas. So, in short, my software would pick up data from a table in a schema and load it up in to the same table in a different schema. Now, I have two issues in creating my target schema and emptying it. I would like this in a batch job. But the oracle scripts you get, the sample schema names are not configurable. So, I tried creating a script, replacing OE with TR_OE, HR with TR_HR and so on. However, this approach is kind of irritating coz the sample schemas are kind of complicated in the way they are created; Oracle creates synonyms, views, materialized views, data types and lot of weird stuff. I would like the target schemas (TR_HR, TR_OE,...) to be empty. But some of the schemas have circular references, which would not allow me to delete data. The only work around seems to be removing certain foreign keys, deleting data and then adding the constraints back. Is there any easy way to all this, without all this fuss? I would need a complicated data set for my testing (complicated as in tables with triggers, multiple hierarchies.. for instance.. a child table that has children up to 5 levels, a parent table that refers to an IOT table and an IOT table that refers to a non-IOT table etc..). The sample schemas are just about perfect from a data set perspective. The only challenge I see is in automating this whole process of loading up the source schemas, and then creating the target schemas and emptying them. Appreciate your help and suggestions.

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  • Beginner problem with posting data table to JsonResult

    - by ognjenb
    With this script I get data from JsonResult (GetDevicesTable) and put them to table ( id="OrderDevices") <script type="text/javascript"> $(document).ready(function() { $("#getDevices a").click(function() { var Id = $(this).attr("rel"); var rowToMove = $(this).closest("tr"); $.post("/ImportXML/GetDevicesTable", { Id: Id }, function(data) { if (data.success) { //remove row rowToMove.fadeOut(function() { $(this).remove() }); //add row to other table $("#OrderDevices").append("<tr><td>"+ data.DeviceId+ "</td><td>" + data.Id+ "</td><td>" + data.OrderId + "</td></tr>"); } else { alert(data.ErrorMsg); } }, "json"); }); }); <% using (Html.BeginForm()) {%> <table id="OrderDevices" class="data-table"> <tr> <th> DeviceId </th> <th> Id </th> <th> OrderId </th> </tr> </table> <p> <input type="submit" value="Submit" /> </p> <% } %> When click on Submit I need something like this: $(document).ready(function() { $("#submit").click(function() { var Id = $(this).attr("rel"); var DeviceId = $(this).attr(???); var OrderId = $(this).attr(???); var rowToMove = $(this).closest("tr"); $.post("/ImportXML/DevicesActions", { Id: Id, DeviceId:DeviceId, OrderId:OrderId }, function(data) { }, "json"); }); }); I have problem with this script because do not know how post data to this JsonResult: public JsonResult DevicesActions(int Id,int DeviceId,int OrderId) { orderdevice ord = new orderdevice(); ord.Id = Id; ord.OrderId = DeviceId; ord.DeviceId = OrderId; DBEntities.AddToorderdevice(ord); DBEntities.SaveChanges(); }

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  • Persistent (purely functional) Red-Black trees on disk performance

    - by Waneck
    I'm studying the best data structures to implement a simple open-source object temporal database, and currently I'm very fond of using Persistent Red-Black trees to do it. My main reasons for using persistent data structures is first of all to minimize the use of locks, so the database can be as parallel as possible. Also it will be easier to implement ACID transactions and even being able to abstract the database to work in parallel on a cluster of some kind. The great thing of this approach is that it makes possible implementing temporal databases almost for free. And this is something quite nice to have, specially for web and for data analysis (e.g. trends). All of this is very cool, but I'm a little suspicious about the overall performance of using a persistent data structure on disk. Even though there are some very fast disks available today, and all writes can be done asynchronously, so a response is always immediate, I don't want to build all application under a false premise, only to realize it isn't really a good way to do it. Here's my line of thought: - Since all writes are done asynchronously, and using a persistent data structure will enable not to invalidate the previous - and currently valid - structure, the write time isn't really a bottleneck. - There are some literature on structures like this that are exactly for disk usage. But it seems to me that these techniques will add more read overhead to achieve faster writes. But I think that exactly the opposite is preferable. Also many of these techniques really do end up with a multi-versioned trees, but they aren't strictly immutable, which is something very crucial to justify the persistent overhead. - I know there still will have to be some kind of locking when appending values to the database, and I also know there should be a good garbage collecting logic if not all versions are to be maintained (otherwise the file size will surely rise dramatically). Also a delta compression system could be thought about. - Of all search trees structures, I really think Red-Blacks are the most close to what I need, since they offer the least number of rotations. But there are some possible pitfalls along the way: - Asynchronous writes -could- affect applications that need the data in real time. But I don't think that is the case with web applications, most of the time. Also when real-time data is needed, another solutions could be devised, like a check-in/check-out system of specific data that will need to be worked on a more real-time manner. - Also they could lead to some commit conflicts, though I fail to think of a good example of when it could happen. Also commit conflicts can occur in normal RDBMS, if two threads are working with the same data, right? - The overhead of having an immutable interface like this will grow exponentially and everything is doomed to fail soon, so this all is a bad idea. Any thoughts? Thanks! edit: There seems to be a misunderstanding of what a persistent data structure is: http://en.wikipedia.org/wiki/Persistent_data_structure

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  • how to check if internal storage file has any data

    - by user3720291
    public class Save extends Activity { int levels = 2; int data_block = 1024; //char[] data = new char[] {'0', '0'}; String blankval = "0"; String targetval = "0"; String temp; String tempwrite; String string = "null"; TextView tex1; TextView tex2; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.save); Intent intent = getIntent(); Bundle b = intent.getExtras(); tex1 = (TextView) findViewById(R.id.textView1); tex2 = (TextView) findViewById(R.id.textView2); if(b!=null) { string =(String) b.get("string"); } loadprev(); save(); } public void save() { if (string.equals("Blank")) blankval = "1"; if (string.equals("Target")) targetval = "1"; temp = blankval + targetval; try { FileOutputStream fos = openFileOutput("data.gds", MODE_PRIVATE); fos.write(temp.getBytes()); fos.close(); } catch (FileNotFoundException e) {e.printStackTrace();} catch (IOException e) {e.printStackTrace();} tex1.setText(blankval); tex2.setText(targetval); } public void loadprev() { String final_data = ""; try { FileInputStream fis = openFileInput("data.gds"); InputStreamReader isr = new InputStreamReader(fis); char[] data = new char[data_block]; int size; while((size = isr.read(data))>0) { String read_data = String.copyValueOf(data, 0, size); final_data += read_data; data = new char[data_block]; } } catch (FileNotFoundException e) {e.printStackTrace();} catch (IOException e) {e.printStackTrace();} char[] tempread = final_data.toCharArray();; blankval = "" + tempread[0]; targetval = "" + tempread[1]; } } After much tinkering i have finally managed to get my save/load function to work, but it does have an error, pretty much i got it to work then i did a fresh reintall deleting data.gds, afterwards the save/load function crashes because the data.gds file has no previous values. can i use a if statment to check if data.gds has any values in it, if so how do i do it and if not, then what could i use instead?

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  • Programmatically import CSV data to Access

    - by FrustratedWithFormsDesigner
    I have an Access database and the source of data comes from generated CSV files. I'd like to have an easy way for the users to simply select the data file and import it. Import should append the existing data to the data already in the data table. Is there a way in Access to create a file selector and import using saved CSV import settings that are already in the file?

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  • warning about data loss c++/c

    - by Dr Deo
    i am getting a benign warning about possible data loss warning C4244: 'argument' : conversion from 'const int' to 'float', possible loss of data question i remember as if float has a larger precision than int. So how can data be lost if i convert from a smaller data type (int) to a larger data type (float)

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  • Why is cakephp form input stored in $this->data and POST data stored in $this->params['form'] ?

    - by spudnik1979
    the cakephp rest tutorial says that post data should be in $this-data, but I am finding that it is not, but instead inside $this-params['form'] However, when using cakephp form helper in a view, the data is in $this-data. Am I correct to have to check both locations in my controller? It just seems a bit of a waste of extra code. Shouldnt the data appear in one place for whether it came from a rest rest requestor or Cakephp form post? ps im using cakephp 1.3

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  • Passing data between blocks using sinatra

    - by Dan Galipo
    Hi All I'm trying to pass data between blocks using sinatra. For example: @data = Hash.new post "/" do @data[:test] = params.fetch("test").to_s redirect "/tmp" end get "/tmp" do puts @data[:test] end However whenever i get to the tmp block @data is nil and throws an error. Why is that?

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  • Grep and Extract Data in Perl

    - by syker
    I have HTML content stored in a variable. How do I extract data that is found between a set of common tags in the page? For example, I am interested in the data (represented by DATA kept between a set of tags which one line after the other: ... <td class="jumlah">*DATA*</td> <td class="ud"><a href="">*DATA*</a></td> ...

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  • How to implement an offline reader writer lock

    - by Peter Morris
    Some context for the question All objects in this question are persistent. All requests will be from a Silverlight client talking to an app server via a binary protocol (Hessian) and not WCF. Each user will have a session key (not an ASP.NET session) which will be a string, integer, or GUID (undecided so far). Some objects might take a long time to edit (30 or more minutes) so we have decided to use pessimistic offline locking. Pessimistic because having to reconcile conflicts would be far too annoying for users, offline because the client is not permanently connected to the server. Rather than storing session/object locking information in the object itself I have decided that any aggregate root that may have its instances locked should implement an interface ILockable public interface ILockable { Guid LockID { get; } } This LockID will be the identity of a "Lock" object which holds the information of which session is locking it. Now, if this were simple pessimistic locking I'd be able to achieve this very simply (using an incrementing version number on Lock to identify update conflicts), but what I actually need is ReaderWriter pessimistic offline locking. The reason is that some parts of the application will perform actions that read these complex structures. These include things like Reading a single structure to clone it. Reading multiple structures in order to create a binary file to "publish" the data to an external source. Read locks will be held for a very short period of time, typically less than a second, although in some circumstances they could be held for about 5 seconds at a guess. Write locks will mostly be held for a long time as they are mostly held by humans. There is a high probability of two users trying to edit the same aggregate at the same time, and a high probability of many users needing to temporarily read-lock at the same time too. I'm looking for suggestions as to how I might implement this. One additional point to make is that if I want to place a write lock and there are some read locks, I would like to "queue" the write lock so that no new read locks are placed. If the read locks are removed withing X seconds then the write lock is obtained, if not then the write lock backs off; no new read-locks would be placed while a write lock is queued. So far I have this idea The Lock object will have a version number (int) so I can detect multi-update conflicts, reload, try again. It will have a string[] for read locks A string to hold the session ID that has a write lock A string to hold the queued write lock Possibly a recursion counter to allow the same session to lock multiple times (for both read and write locks), but not sure about this yet. Rules: Can't place a read lock if there is a write lock or queued write lock. Can't place a write lock if there is a write lock or queued write lock. If there are no locks at all then a write lock may be placed. If there are read locks then a write lock will be queued instead of a full write lock placed. (If after X time the read locks are not gone the lock backs off, otherwise it is upgraded). Can't queue a write lock for a session that has a read lock. Can anyone see any problems? Suggest alternatives? Anything? I'd appreciate feedback before deciding on what approach to take.

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  • Domain Validation in a CQRS architecture

    - by Jupaol
    Basically I want to know if there is a better way to validate my domain entities. This is how I am planning to do it but I would like your opinion The first approach I considered was: class Customer : EntityBase<Customer> { public void ChangeEmail(string email) { if(string.IsNullOrWhitespace(email)) throw new DomainException(“...”); if(!email.IsEmail()) throw new DomainException(); if(email.Contains(“@mailinator.com”)) throw new DomainException(); } } I actually do not like this validation because even when I am encapsulating the validation logic in the correct entity, this is violating the Open/Close principle (Open for extension but Close for modification) and I have found that violating this principle, code maintenance becomes a real pain when the application grows up in complexity. Why? Because domain rules change more often than we would like to admit, and if the rules are hidden and embedded in an entity like this, they are hard to test, hard to read, hard to maintain but the real reason why I do not like this approach is: if the validation rules change, I have to come and edit my domain entity. This has been a really simple example but in RL the validation could be more complex So following the philosophy of Udi Dahan, making roles explicit, and the recommendation from Eric Evans in the blue book, the next try was to implement the specification pattern, something like this class EmailDomainIsAllowedSpecification : IDomainSpecification<Customer> { private INotAllowedEmailDomainsResolver invalidEmailDomainsResolver; public bool IsSatisfiedBy(Customer customer) { return !this.invalidEmailDomainsResolver.GetInvalidEmailDomains().Contains(customer.Email); } } But then I realize that in order to follow this approach I had to mutate my entities first in order to pass the value being valdiated, in this case the email, but mutating them would cause my domain events being fired which I wouldn’t like to happen until the new email is valid So after considering these approaches, I came out with this one, since I am going to implement a CQRS architecture: class EmailDomainIsAllowedValidator : IDomainInvariantValidator<Customer, ChangeEmailCommand> { public void IsValid(Customer entity, ChangeEmailCommand command) { if(!command.Email.HasValidDomain()) throw new DomainException(“...”); } } Well that’s the main idea, the entity is passed to the validator in case we need some value from the entity to perform the validation, the command contains the data coming from the user and since the validators are considered injectable objects they could have external dependencies injected if the validation requires it. Now the dilemma, I am happy with a design like this because my validation is encapsulated in individual objects which brings many advantages: easy unit test, easy to maintain, domain invariants are explicitly expressed using the Ubiquitous Language, easy to extend, validation logic is centralized and validators can be used together to enforce complex domain rules. And even when I know I am placing the validation of my entities outside of them (You could argue a code smell - Anemic Domain) but I think the trade-off is acceptable But there is one thing that I have not figured out how to implement it in a clean way. How should I use this components... Since they will be injected, they won’t fit naturally inside my domain entities, so basically I see two options: Pass the validators to each method of my entity Validate my objects externally (from the command handler) I am not happy with the option 1 so I would explain how I would do it with the option 2 class ChangeEmailCommandHandler : ICommandHandler<ChangeEmailCommand> { public void Execute(ChangeEmailCommand command) { private IEnumerable<IDomainInvariantValidator> validators; // here I would get the validators required for this command injected, and in here I would validate them, something like this using (var t = this.unitOfWork.BeginTransaction()) { var customer = this.unitOfWork.Get<Customer>(command.CustomerId); this.validators.ForEach(x =. x.IsValid(customer, command)); // here I know the command is valid // the call to ChangeEmail will fire domain events as needed customer.ChangeEmail(command.Email); t.Commit(); } } } Well this is it. Can you give me your thoughts about this or share your experiences with Domain entities validation EDIT I think it is not clear from my question, but the real problem is: Hiding the domain rules has serious implications in the future maintainability of the application, and also domain rules change often during the life-cycle of the app. Hence implementing them with this in mind would let us extend them easily. Now imagine in the future a rules engine is implemented, if the rules are encapsulated outside of the domain entities, this change would be easier to implement

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  • How to model a relationship that NHibernate (or Hibernate) doesn’t easily support

    - by MylesRip
    I have a situation in which the ideal relationship, I believe, would involve Value Object Inheritance. This is unfortunately not supported in NHibernate so any solution I come up with will be less than perfect. Let’s say that: “Item” entities have a “Location” that can be in one of multiple different formats. These formats are completely different with no overlapping fields. We will deal with each Location in the format that is provided in the data with no attempt to convert from one format to another. Each Item has exactly one Location. “SpecialItem” is a subtype of Item, however, that is unique in that it has exactly two Locations. “Group” entities aggregate Items. “LocationGroup” is as subtype of Group. LocationGroup also has a single Location that can be in any of the formats as described above. Although I’m interested in Items by Group, I’m also interested in being able to find all items with the same Location, regardless of which group they are in. I apologize for the number of stipulations listed above, but I’m afraid that simplifying it any further wouldn’t really reflect the difficulties of the situation. Here is how the above could be diagrammed: Mapping Dilemma Diagram: (http://www.freeimagehosting.net/uploads/592ad48b1a.jpg) (I tried placing the diagram inline, but Stack Overflow won't allow that until I have accumulated more points. I understand the reasoning behind it, but it is a bit inconvenient for now.) Hmmm... Apparently I can't have multiple links either. :-( Analyzing the above, I make the following observations: I treat Locations polymorphically, referring to the supertype rather than the subtype. Logically, Locations should be “Value Objects” rather than entities since it is meaningless to differentiate between two Location objects that have all the same values. Thus equality between Locations should be based on field comparisons, not identifiers. Also, value objects should be immutable and shared references should not be allowed. Using NHibernate (or Hibernate) one would typically map value objects using the “component” keyword which would cause the fields of the class to be mapped directly into the database table that represents the containing class. Put another way, there would not be a separate “Locations” table in the database (and Locations would therefore have no identifiers). NHibernate (or Hibernate) do not currently support inheritance for value objects. My choices as I see them are: Ignore the fact that Locations should be value objects and map them as entities. This would take care of the inheritance mapping issues since NHibernate supports entity inheritance. The downside is that I then have to deal with aliasing issues. (Meaning that if multiple objects share a reference to the same Location, then changing values for one object’s Location would cause the location to change for other objects that share the reference the same Location record.) I want to avoid this if possible. Another downside is that entities are typically compared by their IDs. This would mean that two Location objects would be considered not equal even if the values of all their fields are the same. This would be invalid and unacceptable from the business perspective. Flatten Locations into a single class so that there are no longer inheritance relationships for Locations. This would allow Locations to be treated as value objects which could easily be handled by using “component” mapping in NHibernate. The downside in this case would be that the domain model becomes weaker, more fragile and less maintainable. Do some “creative” mapping in the hbm files in order to force Location fields to be mapped into the containing entities’ tables without using the “component” keyword. This approach is described by Colin Jack here. My situation is more complicated than the one he describes due to the fact that SpecialItem has a second Location and the fact that a different entity, LocatedGroup, also has Locations. I could probably get it to work, but the mappings would be non-intuitive and therefore hard to understand and maintain by other developers in the future. Also, I suspect that these tricky mappings would likely not be possible using Fluent NHibernate so I would use the advantages of using that tool, at least in that situation. Surely others out there have run into similar situations. I’m hoping someone who has “been there, done that” can share some wisdom. :-) So here’s the question… Which approach should be preferred in this situation? Why?

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  • How many tiers should my models have in a DB driven web app?

    - by Hanno Fietz
    In my experience, the "Model" in MVC is often not really a single layer. I would regularly have "backend" models and "frontend" models, where the backend ones would have properties that I want to hide from the UI code, and the frontend ones have derived or composite properties which are more meaningful in the context of the UI. Recently, I have started to introduce a third layer in between when database normalization created tables that did not really match the conceptual domain objects anymore. In those projects I have model classes that are equivalent with the DB structure, these become components of objects that represent the domain model, and finally these are filtered and amended for displaying information to the user. Are there patterns or guidelines for how, when and why to organize the data model across application layers?

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