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  • Custom Django Field is deciding to work as ForiegnKey for no reason

    - by Joe Simpson
    Hi, i'm making a custom field in Django. There's a problem while trying to save it, it's supposed to save values like this 'user 5' and 'status 9' but instead in the database these fields show up as just the number. Here is the code for the field: def find_key(dic, val): return [k for k, v in dic.items() if v == val][0] class ConnectionField(models.TextField): __metaclass__ = models.SubfieldBase serialize = False description = 'Provides a connection for an object like User, Page, Group etc.' def to_python(self, value): if type(value) != unicode: return value value = value.split(" ") if value[0] == "user": return User.objects.get(pk=value[1]) else: from social.models import connections return get_object_or_404(connections[value[0]], pk=value[1]) def get_prep_value(self, value): from social.models import connections print value, "prep" if type(value) == User: return "user %s" % str(value.pk) elif type(value) in connections.values(): o= "%s %s" % (find_key(connections, type(value)), str(value.pk)) print o, "return" return o else: print "CONNECTION ERROR!" raise TypeError("Value is not connectable!") Connection is just a dictionary with the "status" text linked up to the model for a StatusUpdate. I'm saving a model like this which is causing the issue: Relationship.objects.get_or_create(type="feedback",from_user=request.user,to_user=item) Please can someone help, Many Thanks Joe *_*

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  • sybase - values from one table that aren't on another, on opposite ends of a 3-table join

    - by Lazy Bob
    Hypothetical situation: I work for a custom sign-making company, and some of our clients have submitted more sign designs than they're currently using. I want to know what signs have never been used. 3 tables involved: table A - signs for a company sign_pk(unique) | company_pk | sign_description 1 --------------------1 ---------------- small 2 --------------------1 ---------------- large 3 --------------------2 ---------------- medium 4 --------------------2 ---------------- jumbo 5 --------------------3 ---------------- banner table B - company locations company_pk | company_location(unique) 1 ------|------ 987 1 ------|------ 876 2 ------|------ 456 2 ------|------ 123 table C - signs at locations (it's a bit of a stretch, but each row can have 2 signs, and it's a one to many relationship from company location to signs at locations) company_location | front_sign | back_sign 987 ------------ 1 ------------ 2 987 ------------ 2 ------------ 1 876 ------------ 2 ------------ 1 456 ------------ 3 ------------ 4 123 ------------ 4 ------------ 3 So, a.company_pk = b.company_pk and b.company_location = c.company_location. What I want to try and find is how to query and get back that sign_pk 5 isn't at any location. Querying each sign_pk against all of the front_sign and back_sign values is a little impractical, since all the tables have millions of rows. Table a is indexed on sign_pk and company_pk, table b on both fields, and table c only on company locations. The way I'm trying to write it is along the lines of "each sign belongs to a company, so find the signs that are not the front or back sign at any of the locations that belong to the company tied to that sign." My original plan was: Select a.sign_pk from a, b, c where a.company_pk = b.company_pk and b.company_location = c.company_location and a.sign_pk *= c.front_sign group by a.sign_pk having count(c.front_sign) = 0 just to do the front sign, and then repeat for the back, but that won't run because c is an inner member of an outer join, and also in an inner join. This whole thing is fairly convoluted, but if anyone can make sense of it, I'll be your best friend.

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  • Referencing not-yet-defined variables - Java

    - by user2537337
    Because I'm tired of solving math problems, I decided to try something more engaging with my very rusty (and even without the rust, very basic) Java skills. I landed on a super-simple people simulator, and thus far have been having a grand time working through the various steps of getting it to function. Currently, it generates an array of people-class objects and runs a for loop to cycle through a set of actions that alter the relationships between them, which I have stored in a 2d integer array. When it ends, I go look at how much they all hate each other. Fun stuff. Trouble has arisen, however, because I would like the program to clearly print what action is happening when it happens. I thought the best way to do this would be to add a string, description, to my "action" class (which stores variables for the actor, reactor, and the amount the relationship changes). This works to a degree, in that I can print a generic message ("A fight has occurred!") with no problem. However, ideally I would like it to be a little more specific ("Person A has thrown a rock at Person B's head!"). This latter goal is proving more difficult: attempting to construct an action with a description string that references actor and reactor gets me a big old error, "Cannot reference field before it is defined." Which makes perfect sense. I believe I'm not quite in programmer mode, because the only other way I can think to do this is an unwieldy switch statement that negates the need for each action to have its own nicely-packaged description. And there must be a neater way. I am not looking for examples of code, only a push in the direction of the right concept to handle this.

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  • Hibernate collection mapping Problem

    - by Geln Yang
    Hi, There is a table Item like, code,name 01,parent1 02,parent2 0101,child11 0102,child12 0201,child21 0202,child22 Create a java object and hbm xml to map the table.The Item.parent is a Item whose code is equal to the first two characters of its code : class Item{ String code; String name; Item parent; List<Item> children; .... setter/getter.... } <hibernate-mapping> <class name="Item" table="Item"> <id name="code" length="4" type="string"> <generator class="assigned" /> </id> <property name="name" column="name" length="50" not-null="true" /> <many-to-one name="parent" class="Item" not-found="ignore"> <formula> <![CDATA[ (select i.code,r.name from Item i where (case length(code) when 4 then i.code=SUBSTRING(code,1,2) else false end)) ]]> </formula> </many-to-one> <bag name="children"></bag> </class> </hibernate-mapping> I try to use formula to define the many-to-one relationship,but it doesn't work!Is there something wrong?Or is there other method? Thanks! ps,I use mysql database.

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  • Designing small comparable objects

    - by Thomas Ahle
    Intro Consider you have a list of key/value pairs: (0,a) (1,b) (2,c) You have a function, that inserts a new value between two current pairs, and you need to give it a key that keeps the order: (0,a) (0.5,z) (1,b) (2,c) Here the new key was chosen as the average between the average of keys of the bounding pairs. The problem is, that you list may have milions of inserts. If these inserts are all put close to each other, you may end up with keys such to 2^(-1000000), which are not easily storagable in any standard nor special number class. The problem How can you design a system for generating keys that: Gives the correct result (larger/smaller than) when compared to all the rest of the keys. Takes up only O(logn) memory (where n is the number of items in the list). My tries First I tried different number classes. Like fractions and even polynomium, but I could always find examples where the key size would grow linear with the number of inserts. Then I thought about saving pointers to a number of other keys, and saving the lower/greater than relationship, but that would always require at least O(sqrt) memory and time for comparison. Extra info: Ideally the algorithm shouldn't break when pairs are deleted from the list.

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  • connecting to secure database from website host

    - by jim
    Hello all, I've got a requirement to both read and write data via a .net webservice to a sqlserver database that's on a private network. this database is currently accessed via a vpn connection by remote client software (on standard desktop machines) to get latest product prices and to upload product stock sales. I've been tasked with finding a way to centralise this access from a webservice that the clients then access, rather than them using the vpn route to connect directly to the database. My question is related to my .net service's relationship to the sqlserver database. What are the options for connecting to a private network vpn from a domain host in order to achive the functionality of allowing the webservice to both read and write data to the database. For now, I'm not too concerned about the client connectivity and security (tho i appreciate that this will have to be worked out too), I'm really just interested in discovering the options available in order to allow my .net webservice to connect to the private network in as painless and transparent a way as posible. The option of switching the database onto public hosting is not an option, so I have to work with the sdcenario as described above for now, unless there's a compelling rationale presented to do otherwise. thanks all... jim

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  • Using IAM for user authentication

    - by mdavis6890
    I've read lots and lots of posts that touch on what I think should be a very common use case - but without finding exactly what I want, or a simple reason why it can't be done. I have some files on S3. I want to be able to grant certain users access to certain files, via a front end that I build. So far, I've made it work this way: I built the front end in Django, using it's built-in Users and Groups I have a model for Buckets, in which I mirror my S3 buckets. I have a m2m relationship from groups to buckets representing the S3 permissions. The user logs in and authenticates against Django's users. I grab from Django the list of buckets that the user is allowed to see I use boto to grab a list of links to files from those buckets and display to user. This works, but isn't ideal, and also just doesn't feel right. I've got to keep a mirror of the buckets, and I also have to maintain my own list of user/passwords and permissions, when AWS already has all that built in. What I really want is to simply create the users in IAM and use group permissions in IAM to control access to the S3 buckets. No duplication of data or function. My app would request a UN/PW from the user and use that to connect to IAM/S3 to pull the list of buckets and files, then display links to the user. Simple. How can I, or why can't I? Am I looking at this the wrong way? What's the "right" way to address this (I assume) very common use case?

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  • How can I set the tab on a webpage depending on which page you come from in ASP.Net MVC?

    - by uriDium
    I have a rather large entity. It has a parent relationship with many different child tables. Each of the child tables I have represented as a tab (luckily it makes sense and looks nice and makes things easier to navigate). If the users wants to add a new child row, they go the particular tab, and there they see a list of rows which is owned by the parent and they can do the usual CRUD. The CRUD takes them to a new controller and action and passes the ID of the parent to the action. (This is as far as I can tell what I was meant to do, any other ideas??) When they have finsihed they click save and it takes them back to the original page BUT I want it to automatically go to the right tab. How can I do this? I am using Jquery UI tabs, ASP.Net MVC 2.0. One idea I had was to just go back to the bookmark (the href part with the #, for e.g. /Parent/Details/4/#tabname). Apparently JQuery UI tabs can handle this. Or to set the tab name as part of the query string (/Parent/Details/4?tab=name) What is the best practise here?

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  • connecting to secure database on private network from website host

    - by jim
    Hello all, I've got a requirement to both read and write data via a .net webservice to a sqlserver database that's on a private network. this database is currently accessed via a vpn connection by remote client software (on standard desktop machines) to get latest product prices and to upload product stock sales. I've been tasked with finding a way to centralise this access from a webservice that the clients then access, rather than them using the vpn route to connect directly to the database. My question is related to my .net service's relationship to the sqlserver database. What are the options for connecting to a private network vpn from a domain host in order to achive the functionality of allowing the webservice to both read and write data to the database. For now, I'm not too concerned about the client connectivity and security (tho i appreciate that this will have to be worked out too), I'm really just interested in discovering the options available in order to allow my .net webservice to connect to the private network in as painless and transparent a way as posible. [edit] the webservice will also be available to the retail website in order for it to lookup product info as well as allocate stock transfers to the same sqlserver db. it will therefore be located on the same domain as the retail site The option of switching the database onto public hosting is not feasible, so I have to work with the scenario as described above for now, unless there's a compelling rationale presented to do otherwise. thanks all... jim

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  • How can I recurse up a DOM tree?

    - by smartdirt
    So I have a series of nested ul elements as part of a tree like below: <ul> <li> <ul> <li>1.1</li> <li>1.2</li> </ul> <ul> <li>2.1</li> <li> <ul> <li>2.2</li> </ul> </li> </ul> <ul> <li>3.1</li> <li>3.2</li> </ul> </li> </ul> Let's say when 3.1 is the selected node and when the user clicks previous the selected node should then be 2.2. The bad news is that there could be any number of levels deep. How can I find the previous node (li) in relationship to the currently selected node using jquery?

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  • Hibernate collection mapping challenge

    - by Geln Yang
    Hi, There is a table Item like, code,name 01,parent1 02,parent2 0101,child11 0102,child12 0201,child21 0202,child22 Create a java object and hbm xml to map the table.The Item.parent is a Item whose code is equal to the first two character of its code : class Item{ string code; string name; Item parent; List<Item> children; .... setter/getter.... } <hibernate-mapping> <class name="Item" table="Item"> <id name="code" length="4" type="string"> <generator class="assigned" /> </id> <property name="name" column="name" length="50" not-null="true" /> <!--====================================== --> <many-to-one name="parent" class="Item" not-found="ignore"></many-to-one> <bag name="children"></bag> <!--====================================== --> </class> </hibernate-mapping> How to definition the mapping relationship? Thanks!

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  • SQL n:m Inheritance join

    - by Nightmares
    I want to join a table which contains n:m relationship between groups. (Groups are defined in a separate table). This table only has entries listing a member_group_id and a parent_group_id. Given this structure: id(int) | member_group_id(int) | parent_group_id(int) The "base" query looks like this: select p1.group_id, p2.group_id, p1.member_group_id, p2.member_group_id from group_member_group as p1 join group_member_group as p2 on p2.member_group_id = p1.member_group_id The "base" query correctly shows all relationships (I checked by doing it manually.) The problem is when I try to apply a where clause to this query to filter for a specific group as "point of origin" (the first group for which I want all parent groups) it returns only the closest parents. For example like this: select p1.group_id, p2.group_id, p1.member_group_id, p2.member_group_id from group_member_group as p1 join group_member_group as p2 on p2.member_group_id = p1.member_group_id where p1.group_id = 1 Can anyone give a clue how I can fix this? Or a different approach to realize this. (I suppose I could always do this in my C++ source code on the server side but I would have to transfer a entire table which has a high growth potential to the application server.) UPDATE: select p1.group_id, p2.group_id, p1.member_group_id, p2.member_group_id from group_member_group as p1 join group_member_group as p2 on p2.group_id = p1.member_group_id Typing mistake confirmed. Now I don't get past first level of inheritance period. Thanks at denied for pointing that out.

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  • NoSQL for filesystem storage organization and replication?

    - by wheaties
    We've been discussing design of a data warehouse strategy within our group for meeting testing, reproducibility, and data syncing requirements. One of the suggested ideas is to adapt a NoSQL approach using an existing tool rather than try to re-implement a whole lot of the same on a file system. I don't know if a NoSQL approach is even the best approach to what we're trying to accomplish but perhaps if I describe what we need/want you all can help. Most of our files are large, 50+ Gig in size, held in a proprietary, third-party format. We need to be able to access each file by a name/date/source/time/artifact combination. Essentially a key-value pair style look-up. When we query for a file, we don't want to have to load all of it into memory. They're really too large and would swamp our server. We want to be able to somehow get a reference to the file and then use a proprietary, third-party API to ingest portions of it. We want to easily add, remove, and export files from storage. We'd like to set up automatic file replication between two servers (we can write a script for this.) That is, sync the contents of one server with another. We don't need a distributed system where it only appears as if we have one server. We'd like complete replication. We also have other smaller files that have a tree type relationship with the Big files. One file's content will point to the next and so on, and so on. It's not a "spoked wheel," it's a full blown tree. We'd prefer a Python, C or C++ API to work with a system like this but most of us are experienced with a variety of languages. We don't mind as long as it works, gets the job done, and saves us time. What you think? Is there something out there like this?

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  • Hibernate mapping Problem

    - by Geln Yang
    Hi, There is a table Item like, code,name 01,parent1 02,parent2 0101,child11 0102,child12 0201,child21 0202,child22 Create a java object and hbm xml to map the table.The Item.parent is a Item whose code is equal to the first two characters of its code : class Item{ String code; String name; Item parent; List<Item> children; .... setter/getter.... } <hibernate-mapping> <class name="Item" table="Item"> <id name="code" length="4" type="string"> <generator class="assigned" /> </id> <property name="name" column="name" length="50" not-null="true" /> <many-to-one name="parent" class="Item" not-found="ignore"> <formula> <![CDATA[ (select i.code,r.name from Item i where (case length(code) when 4 then i.code=SUBSTRING(code,1,2) else false end)) ]]> </formula> </many-to-one> <bag name="children"></bag> </class> </hibernate-mapping> I try to use formula to define the many-to-one relationship,but it doesn't work!Is there something wrong?Or is there other method? Thanks! ps,I use mysql database.

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  • How to use AFIncrementalStore to binding with a NSManagedObject

    - by Matrosov Alexander
    I am searching for more information on how to use AFIncrementalStore. I need to know how to implement it step by step. Please don't down vote it, because of many resources, I really need help with this. If I understood right AFIncrementalStore it is a layer for fetching data from the server and for the mapping data model. Am I right? So I have few URL that I need to mapping into my local model. All of them use GET requests. For example base_url/api/categories I get this string in response: [{"category":{"name":"3d max","id":"1111001","users":[]}}, {"category":{"name":"photoshop","id":"1111002","users":[]}}, {"category":{"name":"auto cad","id":"1111003","users":[]}}] So I have a question how I can binding my local db with this data using AFIncrementalStore. Also if you can see there are relationships in the response string that are connected to uses. The array for users will contain id that is correspond to concert users. So I think second question is how to point that model has to have relationship.

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  • How to design data storage for partitioned tagging system?

    - by Morgan Cheng
    How to design data storage for huge tagging system (like digg or delicious)? There is already discussion about it, but it is about centralized database. Since the data is supposed to grow, we'll need to partition the data into multiple shards soon or later. So, the question turns to be: How to design data storage for partitioned tagging system? The tagging system basically has 3 tables: Item (item_id, item_content) Tag (tag_id, tag_title) TagMapping(map_id, tag_id, item_id) That works fine for finding all items for given tag and finding all tags for given item, if the table is stored in one database instance. If we need to partition the data into multiple database instances, it is not that easy. For table Item, we can partition its content with its key item_id. For table Tag, we can partition its content with its key tag_id. For example, we want to partition table Tag into K databases. We can simply choose number (tag_id % K) database to store given tag. But, how to partition table TagMapping? The TagMapping table represents the many-to-many relationship. I can only image to have duplication. That is, same content of TagMappping has two copies. One is partitioned with tag_id and the other is partitioned with item_id. In scenario to find tags for given item, we use partition with tag_id. If scenario to find items for given tag, we use partition with item_id. As a result, there is data redundancy. And, the application level should keep the consistency of all tables. It looks hard. Is there any better solution to solve this many-to-many partition problem?

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  • What do you mean by the expressiveness in programming lanuguage?

    - by prosseek
    I see a lot of the word 'expressiveness' when people want to stress one language is better than the other. But I don't see exactly what they mean by it. Is it the verboseness/succinctness? I mean, if one language can write down something shorter than the other, does that mean expressiveness? Please refer to my other question - http://stackoverflow.com/questions/2411772/article-about-code-density-as-a-measure-of-programming-language-power Is it the power of the language? Paul Graham says that one language is more powerful than the other language in a sense that one language can do that the other language can't do (for example, LISP can do something with macro that the other language can't do). Is it just something that makes life easier? Regular expression can be one of the examples. Is it a different way of solving the same problem: something like SQL to solve the search problem? What do you think about the expressiveness of a programming lanuage? Can you show the expressiveness using some code? What's the relationship with the expressiveness and DSL? Do people come up with DSL to get the expressiveness?

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  • C# Dataset Dynamically Add DataColumn

    - by Wesley
    I am trying to add a extra column to a dataset after a query has completed. I have a database relationship of the following: Employees / \ Groups EmployeeGroups Empoyees holds all the data for that individual, I'll name the unique key the UserID. Groups holds all the groups that a employee can be a part of, i.e. Super User, Admin, User; etc. I will name the unique key GroupID EmployeeGroups holds all the associations of which groups each employee belongs too. (UserID | GroupID) What I am trying to accomplish is after querying for a all users I want to loop though each user and add what groups that user is a part of by adding a new column to the dataset named 'Groups' which is a string to insert the values of the next query to get all the groups that user is a part of. Then by user of databinding populate a listview with all employees and their group associations My code is as follows; Position 5 is the new column I am trying to add to the dataset. string theQuery = "select UserID, FirstName, LastName, EmployeeID, Active from Employees"; DataSet theEmployeeSet = itsDatabase.runQuery(theQuery); DataColumn theCol = new DataColumn("Groups", typeof(string)); theEmployeeSet.Tables[0].Columns.Add(theCol); foreach (DataRow theRow in theEmployeeSet.Tables[0].Rows) { theRow.ItemArray[5] = "1234"; } At the moment, the code will create the new column but when i assign the data to that column nothing will be assigned, what am I missing? If there is any further explination or information I can provide, please let me know. Thank you all

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  • Core Data Predicates with Subclassed NSManagedObjects

    - by coneybeare
    I have an AUDIO class. This audio has a SOUND_A subclass and a SOUND_B subclass. This is all done correctly and is working fine. I have another model, lets call it PLAYLIST_JOIN, and this can contain (in the real world) SOUND_A's and SOUND_B's, so we give it a relationship of AUDIO and PLAYLIST. This all works in the app. The problem I am having now is querying the PLAYLIST_JOIN table with an NSPredicate. What I want to do is find an exact PLAYLIST_JOIN item by giving it 2 keys in the predicate sound_a._sound_a_id = %@ && playlist.playlist_id = %@ and sound_b.sound_b_id = %@ && playlist.playlist_id = %@ The main problem is that because the table does not store sound_a and sound_b, but stored audio, I cannot use this syntax. I do not have the option of reorganizing the sound_a and sound_b to use the same _id attribute name, so how do I do this? Can I pass a method to the predicate? something like this: [audio getID] = %@ && playlist_id = %@

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  • Appengine JDO dataclasses to python model

    - by M.A. Cape
    Does anyone have tried to implement an app in GAE having both java and python? I have an existing app and my front end is in java. Now I want to use the existing datastore to be interfaced by python. My problem is i don't know how to define the relationships and model that would be equivalent to the one in java. I have tried the one-to-many relationship in python but when stored in the datastore, the fields are different than the one-to-many of java. My data classes are as follows. //one-to-many owned Parent Class public class Parent{ @PrimaryKey @Persistent private String unitID; //some other fields... @Persistent @Order(extensions = @Extension(vendorName="datanucleus", key="list-ordering", value="dateCreated desc")) private List <Child> child; //methods & constructors were omitted } Child public class Child{ @PrimaryKey @Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY) private Key uId; @Persistent private String name; /* etc... */ }

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  • Need to exclude results in a MySQL query where two table fields are not of certain values (brain far

    - by DondeEstaMiCulo
    I don't know if I'm just burnt out and can't think, or what... But I can't seem to make this work right... (We're using MySQL 5.1...) I have two tables which have some transactional stuff stored in them. There will be many records per user_id in each table. Table1 and Table2 have a one-to-one relationship with each other. I want to pull records from both tables, but I want to exclude records which have certain values in both tables. I don't care if they both don't have these values, or if just one does, but both tables should not have both values. (Does this make any sense? lol) For example: SELECT t1.id, t1.type, t2.name FROM table1 t1 INNER JOIN table2 t2 ON table.xid = table2.id WHERE t1.user_id = 100 AND (t1.type != 'FOO' AND t2.name != 'BAR') So t1.type is type ENUM with about 10 different options, and t2.name is also type ENUM with 2 options. My expected results would look a little like: 1, FOO, YUM 2, BOO, BAR 3, BOO, YUM But instead, all I'm getting is: 3, BOO, YUM Because it's filtering out all records which has 'FOO' as the type, and 'BAR' as the name. I keep waiting for that D'oh! moment where it hits me and I feel like an idiot for not realizing what I'm doing wrong. But it hasn't come. And I still feel like an idiot, lol. I appreciate any light any of you can shed on this! Many thanks in advance for the help!

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  • customer.name joining transactions.name vs. customer.id [serial] joining transactions.id [integer]

    - by Frank Computer
    INFORMIX-SQL 7.32 Pawnshop Application: one-to-many relationship where each customer (master) can have many transactions (detail). customer( id serial, pk_name char(30), {PATERNAL-NAME MATERNAL-NAME, FIRST-NAME MIDDLE-NAME} [...] ); unique index on id; unique cluster index on name; transaction( fk_name char(30), ticket_number serial, [...] ); dups cluster index on fk_name; unique index on ticket_number; Several people have told me this is not the correct way to join master to detail. They said I should always join customer.id[serial] to transactions.id[integer]. When a customer pawns merchandise, clerk queries the master using wildcards on name. The query usually returns several customers, clerk scrolls until locating the right name, enters a 'D' to change to detail transactions table, all transactions are automatically queried, then clerk enters an 'A' to add a new transaction. The problem with using customer.id joining transaction.id is that although the customer table is maintained in sorted name order, clustering the transaction table by fk_id groups the transactions by fk_id, but they are not in the same order as the customer name, so when clerk is scrolling through customer names in the master, the system has to jump allover the place to locate the clustered transactions belonging to each customer. As each new customer is added, the next id is assigned to that customer, but new customers dont show up in alphabetical order. I experimented using id joins and confirmed the decrease in performance. How can I use id joins instead of name joins and still preserve the clustered transaction order by name if transactions has no name column?

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  • Database schema for a library

    - by ABach
    Hi all - I'm designing a library management system for a department at my university and I wanted to enlist your eyes on my proposed schema. This post is primarily concerned with how we store multiple copies of each book; something about what I've designed rubs me the wrong way, and I'm hoping you all can point out better ways to tackle things. For dealing with users checking out books, I've devised three tables: book, customer, and book_copy. The relationships between these tables are as follows: Every book has many book_copies (to avoid duplicating the book's information while storing the fact that we have multiple copies of that book). Every user has many book_copies (the other end of the relationship) The tables themselves are designed like this: ------------------------------------------------ book ------------------------------------------------ + id + title + author + isbn + etc. ------------------------------------------------ ------------------------------------------------ customer ------------------------------------------------ + id + first_name + first_name + email + address + city + state + zip + etc. ------------------------------------------------ ------------------------------------------------ book_copy ------------------------------------------------ + id + book_id (FK to book) + customer_id (FK to customer) + checked_out + due_date + etc. ------------------------------------------------ Something about this seems incorrect (or at least inefficient to me) - the perfectionist in me feels like I'm not normalizing this data correctly. What say ye? Is there a better, more effective way to design this schema? Thanks!

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  • SQL Grouping with multiple joins combining results incorrectly

    - by Matt
    Hi I'm having trouble with my query combining records when it shouldn't. I have two tables Authors and Publications, they are related by Publication ID in a many to many relationship. As each author can have many publications and each publication has many Authors. I want my query to return every publication for a set of authors and include the ID of each of the other authors that have contributed to the publication grouped into one field. (I am working with mySQL) I have tried to picture it graphically below Table: authors Table:publications AuthorID | PublicationID PublicationID | PublicationName 1 | 123 123 | A 1 | 456 456 | B 2 | 123 789 | C 2 | 789 3 | 123 3 | 456 I want my result set to be the following AuthorID | PublicationID | PublicationName | AllAuthors 1 | 123 | A | 1,2,3 1 | 456 | B | 1,3 2 | 123 | A | 1,2,3 2 | 789 | C | 2 3 | 123 | A | 1,2,3 3 | 456 | B | 1,3 This is my query Select Author1.AuthorID, Publications.PublicationID, Publications.PubName, GROUP_CONCAT(TRIM(Author2.AuthorID)ORDER BY Author2.AuthorID ASC)AS 'AuthorsAll' FROM Authors AS Author1 LEFT JOIN Authors AS Author2 ON Author1.PublicationID = Author2.PublicationID INNER JOIN Publications ON Author1.PublicationID = Publications.PublicationID WHERE Author1.AuthorID ="1" OR Author1.AuthorID ="2" OR Author1.AuthorID ="3" GROUP BY Author2.PublicationID But it returns the following instead AuthorID | PublicationID | PublicationName | AllAuthors 1 | 123 | A | 1,1,1,2,2,2,3,3,3 1 | 456 | B | 1,1,3,3 2 | 789 | C | 2 It does deliver the desired output when there is only one AuhorID in the where statement. I have not been able to figure it out, does anyone know where i'm going wrong?

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  • Django filters - Using an AllValuesFilter (with a LinkWidget) on a ManyToManyField

    - by magnetix
    This is my first Stack Overflow question, so please let me know if I do anything wrong. I wish to create an AllValues filter on a ManyToMany field using the wonderful django-filters application. Basically, I want to create a filter that looks like it does in the Admin, so I also want to use the LinkWidget too. Unfortunately, I get an error (Invalid field name: 'operator') if I try this the standard way: # Models class Organisation(models.Model): name = models.CharField() ... class Sign(models.Model): name = models.CharField() operator = models.ManyToManyField('Organisation', blank=True) ... # Filter class SignFilter(LinkOrderFilterSet): operator = django_filters.AllValuesFilter(widget=django_filters.widgets.LinkWidget) class Meta: model = Sign fields = ['operator'] I got around this by creating my own filter with the many to many relationship hard coded: # Models class Organisation(models.Model): name = models.CharField() ... class Sign(models.Model): name = models.CharField() operator = models.ManyToManyField('Organisation', blank=True) ... # Filter class MyFilter(django_filters.ChoiceFilter): @property def field(self): cd = {} for row in self.model.objects.all(): orgs = row.operator.select_related().values() for org in orgs: cd[org['id']] = org['name'] choices = zip(cd.keys(), cd.values()) list.sort(choices, key=lambda x:(x[1], x[0])) self.extra['choices'] = choices return super(AllValuesFilter, self).field class SignFilter(LinkOrderFilterSet): operator = MyFilter(widget=django_filters.widgets.LinkWidget) I am new to Python and Django. Can someone think of a more generic/elegant way of doing this?

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