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  • In Django, using __init__() method of non-abstract parent model to record class name of child model

    - by k-g-f
    In my Django project, I have a non-abstract parent model defined as follows: class Parent(models.Model): classType = models.CharField(editable=False,max_length=50) and, say, two children models defined as follows: class ChildA(Parent): parent = models.OneToOneField(Parent,parent_link=True) class ChildB(Parent): parent = models.OneToOneField(Parent,parent_link=True) Each time I create an instance of ChildA or of ChildB, I'd like the classType attribute to be set to the strings "ChildA" or "ChildB" respectively. What I have done is added an _ _ init_ _() method to Parent as follows: class Parent(models.Model): classType = models.CharField(editable=False,max_length=50) def __init__(self,*args,**kwargs): super(Parent,self).__init__(*args,**kwargs) self.classType = self.__class__.__name__ Is there a better way to implement and achieve my desired result? One downside of this implementation is that when I have an instance of the Parent, say "parent", and I want to get the type of the child object linked with "parent", calling "parent.classType" gives me "Parent". In order to get the appropriate "ChildA" or "ChildB" value, I need to write a "_getClassType()" method to wrap a custom sql query.

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  • MySQL UPDATE WHERE IN for each listed value separately?

    - by Tom
    Hi, I've got the following type of SQL: UPDATE photo AS f LEFT JOIN car AS c ON f.car_id=c.car_id SET f.photo_status=1 , c.photo_count=c.photo_count+1 WHERE f.photo_id IN ($ids) Basically, two tables (car & photo) are related. The list in $ids contains unique photo ids, such as (34, 87, 98, 12). With the query, I'm setting the status of each photo in that list to "1" in the photo table and simultaneously incrementing the photo count in the car table for the car at hand. It works but there's one snag: Because the list can contain multiple photo ids that relate to the same car, the photo count only ever gets incremented once. If the list had 10 photos associated with the same car, photo_count would become 1 .... whereas I'd like to increment it to 10. Is there a way to make the incrementation occur for each photo individually through the join, as opposed to MySQL overthinking it for me? I hope the above makes sense. Thanks.

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  • MySQL Group Results by day using timestamp

    - by Webnet
    I need to take the following query and pull the total order counts and sum of the orders grouped by day. I'm storing everything using timestamps. SELECT COUNT(id) as order_count, SUM(price + shipping_price) as order_sum, DAY(FROM_UNIXTIME(created)) as day FROM `order` WHERE '.implode(' AND ', $where).' I need to group by DAY but when I do for this past weekend's sales it takes my order_count and makes it 1 instead of 3. How can I pull the above values grouped by day? NOTE: The implode is used ONLY to define the time period (WHERE created = TIMESTAMP AND <= TIMESTAMP)

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  • How to convet DataTable to List on runtype with out existin class property [closed]

    - by shamim
    Work on VS2010 C#,Have one DataTable ,want to convert this DataTable to List Suppose: Table dt; On run time want to create similar field from a datatable and fill fields in List.There is no existing class for list properties. ListName=TableName List property name=Table column name List Property type=Table column type List items=Table rows Note: Recently work on EF.To fullfill my project requirement, need to give flexibility to use to input and execute ESQL at runtime .I don’t want to put this execute result on datatable or List ,want to put this result on list. List has no existing class and property,don’t want to convert DataTable on list Type:DataRow If have any query please ask,Thanks in advanced.

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  • How to schedule hundreds of thousands of tasks?

    - by wehriam
    We have hundreds of thousands of tasks that need to be run at a variety of arbitrary intervals, some every hour, some every day, and so on. The tasks are resource intensive and need to be distributed across many machines. Right now tasks are stored in a database with an "execute at this time" timestamp. To find tasks that need to be executed, we query the database for jobs that are due to be executed, then update the timestamps when the task is complete. Naturally this leads to a substantial write load on the database. As far as I can tell, we are looking for something to release tasks into a queue at a set interval. (Workers could then request tasks from that queue.) What is the best way to schedule recurring tasks at scale? For what it's worth we're largely using Python, although we have no problems using components (RabbitMQ?) written in other languages.

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  • Retain Site Background and Switch Pages?

    - by yar
    I was about to redo a Rails site today using AJAX so that the background could remain in place. Then I thought, "that would be exactly like using frames," and then I thought about SEO consequences and I dropped the idea entirely and took a look around the Web. It turns out that few sites -- except for Google itself, which has the link bar at the top -- are doing this. It doesn't look impossible to do, but it's not exactly easy. Aside from Ajaxing, you have to think about updating the query-string and having SEO-friendly links (that actually don't work, but rather make background requests via Javascript). Will any of the new technologies -- HTML5, perhaps -- solve this problem and allow us to have a Web with background colors (and other static elements) that do not disappear momentarily between page refreshes? On the other hand, why are few devs doing this with current technologies? Is it just not a big deal, too complicated to implement, or....?

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  • is NATURAL JOIN any better than SELECT FROM WHERE in terms of performance ?

    - by ashy_32bit
    Today I got into a debate with my project manager about Cartesian products. He says a 'natural join' is somehow much better than using 'select from where' because the later cause the db engine to internally perform a Cartesian product but the former uses another approach that prevents this. As far as I know, the natural join syntax is not any different in anyway than 'select from where' in terms of performance or meaning, I mean you can use either based on your taste. SELECT * FROM table1,table2 WHERE table1.id=table2.id SELECT * FROM table1 NATURAL JOIN table2 please elaborate about the first query causing a Cartesian product but the second one being somehow more smart

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  • Use AJAX to check for a new message

    - by Luke
    Quite simply, I need to alert the end user when they have a new private message. From a combination of research and other opinion, I realise I need to use AJAX for this. The mysql query would be SELECT id FROM tbl_messages WHERE to_viewed = 1 So when someone sends a message, I want an alert to popup on the screen to inform the user without a page reload. I have absolutely no idea what I am doing, but know what I want. Really need help with this, AJAX is definitely something I want to improve as it opens up greater possibilities! Thanks

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  • How to map one class against multiple tables with SQLAlchemy?

    - by tote
    Lets say that I have a database structure with three tables that look like this: items - item_id - item_handle attributes - attribute_id - attribute_name item_attributes - item_attribute_id - item_id - attribute_id - attribute_value I would like to be able to do this in SQLAlchemy: item = Item('item1') item.foo = 'bar' session.add(item) session.commit() item1 = session.query(Item).filter_by(handle='item1').one() print item1.foo # => 'bar' I'm new to SQLAlchemy and I found this in the documentation (http://www.sqlalchemy.org/docs/05/mappers.html#mapping-a-class-against-multiple-tables): j = join(items, item_attributes, items.c.item_id == item_attributes.c.item_id). \ join(attributes, item_attributes.c.attribute_id == attributes.c.attribute_id) mapper(Item, j, properties={ 'item_id': [items.c.item_id, item_attributes.c.item_id], 'attribute_id': [item_attributes.c.attribute_id, attributes.c.attribute_id], }) It only adds item_id and attribute_id to Item and its not possible to add attributes to Item object. Is what I'm trying to achieve possible with SQLAlchemy? Is there a better way to structure the database to get the same behaviour of "dynamic columns"?

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  • Most efficient way to Update with Linq2Sql

    - by pranay
    can I update my employee record as given in below function or i have to make query of employee collection first and than i update data public int updateEmployee(App3_EMPLOYEE employee) { DBContextDataContext db = new DBContextDataContext(); db.App3_EMPLOYEEs.Attach(employee); db.SubmitChanges(); return employee.PKEY; } or i have to do this public int updateEmployee(App3_EMPLOYEE employee) { DBContextDataContext db = new DBContextDataContext(); App3_EMPLOYEE emp = db.App3_EMPLOYEEs.Single(e => e.PKEY == employee.PKEY); db.App3_EMPLOYEEs.Attach(employee,emp); db.SubmitChanges(); return employee.PKEY; } But i dont want to use second option is there any efficient way to update data

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  • Considerations when porting a MS VC++ program (single machine) to a rocks cluster

    - by Mel
    I am trying to port a MS VC++ program to run on a rocks cluster! I am not very good with linux but I am eager to learn and I imagine porting it wouldn't be an impossible task for me. However, I do not understand how to take advantage of the cluster nodes. because it seems that the code execute only runs on the front end server (obviously). I have read a little about MPI and its seems like I should use MPI to comminicate between nodes. The program is currently written such that I have a main thread that synchronizes all worker threads. The main thread also recieves commands to manipulate the simulation or query its state. If the simulation is properly setup, communication between executing threads can be significantly minimized. What I don't understand is how do I start the process on the compute nodes and how do I handle failures in nodes? And maybe there should be other things I should also consider when porting my program to run in a cluster?

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  • Why are my Lucene Document results empty?

    - by vegashacker
    I'm running a simple test--trying to index something and then search for it. I index a simple document, but then when a search for a string in it, I get back what looks to be an empty document (it has no fields). Lucene seems to be doing something, because if I search for a word that's not in the document, it returns 0 results. Any reason why Lucene would reliably return a document when it finds one that matches the given query, and yet that document has nothing in it? Thanks! PS: I'm actually running Lucandra (Lucene + Cassandra). That certainly may be a relevant detail, but not sure.

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  • replicating master tables mapping in transaction tables

    - by NoDisplay
    I have three master tables for location information Country {ID, Name} State {ID, Name, CountryID} City {ID, Name, StateID} Now I have one transcation table called Person which hold the person name and his location information. My Question is shall I have only CityID in the Person table like this: Person {ID, Name, CityID}' And have view of join query which give me detail like "Person{ID,Name,City,State,Country}" or Shall I replicate the mapping Person {ID, Name, CityID, StateID, CountryID} Please suggest which do you feel is to be selected and why? if there is any other option available, please suggest. Thanks in advance.

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  • Finding employees specific to department in SQL SERVER 2000(SET BASED)

    - by xyz
    Suppose I have a table (tblEmp) whose structure is like as under Dept Emp d1 e1 d1 e2 d1 e3 d2 e4 d2 e5 d3 e6 If I need to bring the output as Dept DepartmentSpecificEmployees d1 e1,e2,e3 d2 e4,e5 d3 e6 I will write the query as select Dept, stuff((select Emp + ',' from tblEmp t2 where t1.Dept = t2.Dept for xml path(''),1,1,'')DepartmentSpecificEmployees from tblEmp t1 group by Dept But this will work in Sql Server 2005+. How can I achieve the same in Sql Server 2000 without any variable declaration or loop or cursor? If I use COALESCE as an alternative, then I need to use a variable which will defeat the purpose Please help

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  • For LinqToSQL is 0 true or is 1 (for type Bit)?

    - by Vaccano
    I have a column of type Bit (called BBoolVal in this example). I have a LinqToSQL Statement Like this: var query = List<MyClass> myList = _ctx.DBList .Where(x => x.AGuidID == paramID) .Where(x => x.BBoolVal == false); When I look at the sql it ends up like this (I added the spacing and changed the names): SELECT [t0].[Id], [t0].[AGuidID], [t0].[OtherIDID], [t0].[TimeColumn], [t0].[BBoolVal], [t0].[MoreID] FROM [dbo].[MyTable] AS [t0] WHERE (NOT ([t0].[BBoolVal] = 1)) AND ([t0].[AGuidID] = @p0) Because my x.BBoolVal == false translates to [BBoolVal] == 1 I gather that false = 1 (and thus true = 0). I am asking because this seems a bit backwards to me. I am fine to accept it, I just want to be sure.

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  • C# performance of static string[] contains() (slooooow) vs. == operator

    - by Andrew White
    Hiya, Just a quick query: I had a piece of code which compared a string against a long list of values, e.g. if(str == "string1" || str = "string2" || str == "string3" || str = "string4". DoSomething(); And the interest of code clarity and maintainability I changed it to public static string[] strValues = { "String1", "String2", "String3", "String4"}; ... if(strValues.Contains(str) DoSomething(); Only to find the code execution time went from 2.5secs to 6.8secs (executed ca. 200,000 times). I certainly understand a slight performance trade off, but 300%? Anyway I could define the static strings differently to enhance performance? Cheers.

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  • WMI instrinsic events. Resources

    - by Nickolodeon
    Hi. I subscribe to usb inserted event like this select * FROM __INSTANCECREATIONEVENT WITHIN 3 WHERE TARGETINSTANCE ISA Win32_DiskDrive After inserting usb flash it blinks every 3 seconds. This is polling interval and intrinsic events work by polling object that's in query. Now, we know these types of events may be resource expensive. (Putting value greater then 3 sometimes chokes these events and client program doesn't get notified). Are there other ways to do that, so that usb doesn't get scanned all the time? May be there some extrinsic events available? Right now the only solution I see is to unsubscribe from event above once it trigerred and resubscribe to it in __INSTANCEDELETIONEVENT handler. Hm, althought deletionevent will also poll diskdrive controllers(

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  • INSERT INTO othertbl SELECT * tbl

    - by Harry
    Current situation: INSERT INTO othertbl SELECT * FROM tbl WHERE id = '1' So i want to copy a record from tbl to othertbl. Both tables have an autoincremented unique index. Now the new record should have a new index, rather then the value of the index of the originating record else copying results in a index not unique error. A solution would be to not use the * but since these tables have quite some columns i really think it's getting ugly. So,.. is there a better way to copy a record which results in a new record in othertbl which has a new autoincremented index without having to write out all columns in the query and using a NULL value for the index. -hope it makes sense....-

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  • Modifying SQL XML ?olumn

    - by Chinjoo
    I have an XML column in one of my table. For example I have an Employee table with following fields: Name (varhcar) | Address (XML) The Address field is having values like <Address> <Street></Street> <City></City> </Address> I have some n number of rows already in the table. Now I want to insert a new node - Country to all the rows in tha table. With default: <Country>IND</Country>. How can I write the query for this. I want all the existing data to be as it is with adding the country node to all the Address column XML.

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  • Optimizing MySQL queries with IN operator

    - by Arkadiusz Kondas
    I have a MySQL database with a fairly large table where the products are. Each of them has its own id and categoryId field where there is a category id belongs to this product. Now I have a query that pulls out products from given categories such as: SELECT * FROM products WHERE categoryId IN ( 1, 2, 3, 4, 5, 34, 6, 7, 8, 9, 10, 11, 12 ) Of course, come a WHERE clause and ORDER BY sort but not in this thing. Let's say that these products is 250k and the visits are over 100k per day. Under such conditions in the table slow_log registered weight of these queries with large generation time. Do you have any ideas how to optimize the given problem? Table engine is MyISAM.

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  • Strange Locking Behaviour in SQL Server 2005

    - by SQL Learner
    Can anyone please tell me why does the following statement inside a given stored procedure returns repeated results even with locks on the rows used by the first SELECT statement? BEGIN TRANSACTION DECLARE @Temp TABLE ( ID INT ) INSERT INTO @Temp SELECT ID FROM SomeTable WITH (ROWLOCK, UPDLOCK, READPAST) WHERE SomeValue <= 10 INSERT INTO @Temp SELECT ID FROM SomeTable WITH (ROWLOCK, UPDLOCK, READPAST) WHERE SomeValue >= 5 SELECT * FROM @Temp COMMIT TRANSACTION Any values in SomeTable for which SomeValue is between 5 and 10 will be returned twice, even though they were locked in the first SELECT. I thought that locks were in place for the whole transaction, and so I wasn't expecting the query to return repeated results. Why is this happening?

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  • :from parameter in active record find not well designed?

    - by potlee
    i got this error: SQLite3::SQLException: no such column: apis.name: SELECT * FROM examples WHERE ("apis"."name" = 'deep') my code Api.find :all, :from => params[:table_name], :conditions => {:name => 'deep' } I need to make a back end rails application which will be used by a silverlight application. one of the requirements is to fetch simple data from the database. i need to be able to query different tables with the same code.(my app has 2000 tables!) i think it does not make sense for rails to put in "apis" in the WHERE clause. is there any speciic reason for this?

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  • Optimizing Solr for Sorting

    - by devinfoley
    I'm using Solr for a realtime search index. My dataset is about 60M large documents. Instead of sorting by relevance, I need to sort by time. Currently I'm using the sort flag in the query to sort by time. This works fine for specific searches, but when searches return large numbers of results, Solr has to take all of the resulting documents and sort them by time before returning. This is slow, and there has to be a better way. What is the better way?

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  • Oracle Hibernate with in Netbean RCP

    - by jurnaltejo
    All, i have a problem with hibernate using netbean platform 6.8, i have been search around internet, but cannot found the suitable answer This is my story. i am using oracle database as data source of my hibernate entity with ojdbc14.jar driver. First i create hibernate entity tobe wrapped latter in a netbeans module, i tested the hibernate connection configuration and everything just works well. i can connect to oracle database successfuly, every hibernate query works well. Then i wrapped that hibernate entity jar as a netbeans module, create another module to warp my ojdbc14.jar then i test it. and, im using hibernate library dependency that available on netbean platform (netbean 6.8), but unfutornatelly i got oracle sql error saying “no suitable driver for [connection url]” when running the project. thats quite weird since it doesn’t happend when I test it before with out netbean platform. i thought that is related to netbeans lazy loading issue, i am not sure,. any idea ? tq for help

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  • how to sort an existing table in greasemonkey ?

    - by user570512
    i'm writing a greasemonkey user.js for a page with a table in it. (table is 100 rows by 18 columns.) now what i want to do is to make it sortable on column. and also have it run in both chrome and firefox. all searches for answers sofar resulted in suggestions to use jquery/dojo or something alike. can i be done without any external code? after all it's just a matter of replacing the row's in a different order, right? or is that a silly thing to say? the thing is that i'm already using dojo for some query needs but since i want it to run in both firefox and chrome, i just copy paste the whole dojo thing in my script.. also, most of the solutions i found sofar seem to be more for use when building a table. not for altering an existing one. any help is appreciated.

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