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• Django: Set foreign key using integer?

  - by User

  Is there a way to set foreign key relationship using the integer id of a model? This would be for optimization purposes. For example, suppose I have an Employee model: class Employee(models.Model): first_name = models.CharField(max_length=100) last_name = models.CharField(max_length=100) type = models.ForeignKey('EmployeeType') and EmployeeType(models.Model): type = models.CharField(max_length=100) I want the flexibility of having unlimited employee types, but in the deployed application there will likely be only a single type so I'm wondering if there is a way to hardcode the id and set the relationship this way. This way I can avoid a db call to get the EmployeeType object first.

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• MySQL foreign key constraints, cascade delete

  - by Cudos

  Hello. I want to use foreign keys to keep the integrity and avoid orphans (I already use innoDB). How do I make a SQL statment that DELETE ON CASCADE? Secondly, that using DELETE ON CASCADE. E.g. if I delete a category then it would delete products related to that category even though there are other categories related to those products. The pivot table "categories_products" creates a many-to-many relationship between the two other tables. categories - id (INT) - name (VARCHAR 255) products - id - name - price categories_products - categories_id - products_id

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• How to handle Foreign Keys with Entity Framework

  - by Jack Marchetti

  I have two entities. Groups. Pools. A Group can create many pools. So I setup my Pool table to have a GroupID foreign key. My code: using (entity _db = new entity()) { Pool p = new Pool(); p.Name = "test"; p.Group.ID = "5"; _db.AddToPool(p); } This doesn't work. I get a null reference exception on p.Group. How do I go about creating a new "Pool" and associating a GroupID?

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• ASP MVC C#: LINQ Foreign Key Constraint conflicts

  - by wh0emPah

  I'm having a problem with LINQ. I have 2 tables (Parent-child relation) Table1: Events (EventID, Description) Table2: Groups (GroupID, EventID(FK), Description) Now i want to create an Event an and a child. Event e = new Event(); e.Description = "test"; Datacontext.Events.InsertOnSubmit(event) Group g = new Group(); g.Description = "test2"; g.EventID = e.EventID; Datacontext.Groups.InsertOnSubmit(g); Datacontext.SubmitChanges(); When i debug, i can see that after inserting the event. the EventID has gotten a new value (auto increment). But when Datacontext.SubmitChanges(); gets called. I get the following exception "The INSERT statement conflicted with the FOREIGN KEY constraint ... I know this can be solved by creating a relation in the LINQ diagram between Events and groups. And then setting the entity itself. But i don't want to load the events everytime i ask a list of groups. All i need is some way that when inserting the group fails, the event insert won't be comitted in the database. Sorry if this is a bit unclear, My english isn't really good. Thanks in advance!

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• Populating a foreign key table with variable user input

  - by Vincent

  I'm working on a website that will be based on user contributed data, submitted using a regular HTML form. To simplify my question, let's say that there will be two fields in the form: "User Name" and "Country" (this is just an example, not the actual site). There will be two tables in the database : "countries" and "users," with "users.country_id" being a foreign key to the "countries" table (one-to-many). The initial database will be empty. Users from all over the world will submit their names and the countries they live in and eventually the "countries" table will get filled out with all of the country names in the world. Since one country can have several alternative names, input like Chile, Chili, Chilli will generate 3 different records in the countries table, but in fact there is only one country. When I search for records from Chile, Chili and Chilli will not be included. So my question is - what would be the best way to deal with a situation like this, with conditions such that the initial database is empty, no other resources are available and everything is based on user input? How can I organize it in such way that Chile, Chili and Chilli would be treated as one country, with minimum manual interference. What are the best practices when it comes to normalizing user submitted data and is there a scientific term for this? I'm sure this is a common problem. Again, I used country names just to simplify my question, it can be anything that has possible different spellings.

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• Multiple Foreign keys to a single table and single key pointing to more than one table

  - by user1216775

  I need some suggestions from the database design experts here. I have around six foreign keys into a single table (defect) which all point to primary key in user table. It is like: defect (.....,assigned_to,created_by,updated_by,closed_by...) If I want to get information about the defect I can make six joins. Do we have any better way to do it? Another one is I have a states table which can store one of the user-defined set of values. I have defect table and task table and I want both of these tables to share the common state table (New, In Progress etc.). So I created: task (.....,state_id,type_id,.....) defect(.....,state_id,type_id,...) state(state_id,state_name,...) importance(imp_id,imp_name,...) There are many such common attributes along with state like importance(normal, urgent etc), priority etc. And for all of them I want to use same table. I am keeping one flag in each of the tables to differentiate task and defect. What is the best solution in such a case? If somebody is using this application in health domain, they would like to assign different types, states, importances for their defect or tasks. Moreover when a user selects any project I want to display all the types,states etc under configuration parameters section.

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• How do I delete a foreign key in SQLAlchemy?

  - by Travis

  I'm using SQLAlchemy Migrate to keep track of database changes and I'm running into an issue with removing a foreign key. I have two tables, t_new is a new table, and t_exists is an existing table. I need to add t_new, then add a foreign key to t_exists. Then I need to be able to reverse the operation (which is where I'm having trouble). t_new = sa.Table("new", meta.metadata, sa.Column("new_id", sa.types.Integer, primary_key=True) ) t_exists = sa.Table("exists", meta.metadata, sa.Column("exists_id", sa.types.Integer, primary_key=True), sa.Column( "new_id", sa.types.Integer, sa.ForeignKey("new.new_id", onupdate="CASCADE", ondelete="CASCADE"), nullable=False ) ) This works fine: t_new.create() t_exists.c.new_id.create() But this does not: t_exists.c.new_id.drop() t_new.drop() Trying to drop the foreign key column gives an error: 1025, "Error on rename of '.\my_db_name\#sql-1b0_2e6' to '.\my_db_name\exists' (errno: 150)" If I do this with raw SQL, i can remove the foreign key manually then remove the column, but I haven't been able to figure out how to remove the foreign key with SQLAlchemy? How can I remove the foreign key, and then the column?

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• Which Table Should be Master and Child in Database Design

  - by Jason

  I am quickly learning the ins and outs of database design (something that, as of a week ago, was new to me), but I am running across some questions that don't seem immediately obvious, so I was hoping to get some clarification. The question I have right is about foreign keys. As part of my design, I have a Company table. Originally, I had included address information directly within the table, but, as I was hoping to achieve 3NF, I broke out the address information into its own table, Address. In order to maintain data integrity, I created a row in Company called "addressId" as an INT and the Address table has a corresponding addressId as its primary key. What I'm a little bit confused about (or what I want to make sure I'm doing correctly) is determining which table should be the master (referenced) table and which should be the child (referencing) table. When I originally set this up, I made the Address table the master and the Company the child. However, I now believe this is wrong due to the fact that there should be only one address per Company and, if a Company row is deleted, I would want the corresponding Address to be removed as well (CASCADE deletion). I may be approaching this completely wrong, so I would appreciate any good rules of thumb on how to best think about the relationship between tables when using foreign keys. Thanks!

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• How should I define a composite foreign key for domain constraints in the presence of surrogate keys

  - by Samuel Danielson

  I am writing a new app with Rails so I have an id column on every table. What is the best practice for enforcing domain constraints using foreign keys? I'll outline my thoughts and frustration. Here's what I would imagine as "The Rails Way". It's what I started with. Companies: id: integer, serial company_code: char, unique, not null Invoices: id: integer, serial company_id: integer, not null Products: id: integer, serial sku: char, unique, not null company_id: integer, not null LineItems: id: integer, serial invoice_id: integer, not null, references Invoices (id) product_id: integer, not null, references Products (id) The problem with this is that a product from one company might appear on an invoice for a different company. I added a (company_id: integer, not null) to LineItems, sort of like I'd do if only using natural keys and serials, then added a composite foreign key. LineItems (product_id, company_id) references Products (id, company_id) LineItems (invoice_id, company_id) references Invoices (id, company_id) This properly constrains LineItems to a single company but it seems over-engineered and wrong. company_id in LineItems is extraneous because the surrogate foreign keys are already unique in the foreign table. Postgres requires that I add a unique index for the referenced attributes so I am creating a unique index on (id, company_id) in Products and Invoices, even though id is simply unique. The following table with natural keys and a serial invoice number would not have these issues. LineItems: company_code: char, not null sku: char, not null invoice_id: integer, not null I can ignore the surrogate keys in the LineItems table but this also seems wrong. Why make the database join on char when it has an integer already there to use? Also, doing it exactly like the above would require me to add company_code, a natural foreign key, to Products and Invoices. The compromise... LineItems: company_id: integer, not null sku: integer, not null invoice_id: integer, not null does not require natural foreign keys in other tables but it is still joining on char when there is a integer available. Is there a clean way to enforce domain constraints with foreign keys like God intended, but in the presence of surrogates, without turning the schema and indexes into a complicated mess?

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• Does Rails need database-level constraints?

  - by shrimpy

  I have the same problem as in the following post. So I am wondering, why doesn't Rails support generating foreign keys by default? Isn't it necessary? Or are we supposed to do it manually?

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• Limit foreign key choices in select in an inline form in admin

  - by mightyhal

  Edited :-) Hopefully a bit clearer now. The logic is of the model is: A Building has many Rooms A Room may be inside another Room (a closet, for instance--ForeignKey on 'self') A Room can only in inside of another Room in the same building (this is the tricky part) Here's the code I have: #spaces/models.py from django.db import models class Building(models.Model): name=models.CharField(max_length=32) def __unicode__(self): return self.name class Room(models.Model): number=models.CharField(max_length=8) building=models.ForeignKey(Building) inside_room=models.ForeignKey('self',blank=True,null=True) def __unicode__(self): return self.number and: #spaces/admin.py from ex.spaces.models import Building, Room from django.contrib import admin class RoomAdmin(admin.ModelAdmin): pass class RoomInline(admin.TabularInline): model = Room extra = 2 class BuildingAdmin(admin.ModelAdmin): inlines=[RoomInline] admin.site.register(Building, BuildingAdmin) admin.site.register(Room) The inline will display only rooms in the current building (which is what I want). The problem, though, is that for the inside_room drop down, it displays all of the rooms in the Rooms table (including those in other buildings). In the inline of rooms, I need to limit the inside_room choices to only rooms which are in the current building being displayed by the main form. I can't figure out a way to do it with either a limit_choices_to in the model, nor can I figure out how exactly to override the admin's inline formset properly (I feel like I should be somehow create a custom inline form, pass the building_id of the main form to the custom inline, then limit the queryset for the field's choices based on that--but I just can't wrap my head around how to do it). Maybe this is too complex for the admin site, but it seems like something that would be generally useful... Thanks again for your help!

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• Language of variable names? (native foreign language speakers)

  - by Jj

  We are a spanish speaking development team, we code in django and we all are pretty fluent in english, as all documentation, sample code, APIs, etc come in english. On our last project we chose to name all the variables, class names, modules, files and such in english, even though the whole application was in spanish, we kept a strings file where all our spanish was stored. We did this because it seemed more natural to read the whole code in one language, since keywords, constructs and dependencies have names in english. On new projects we are starting, we are having second thoughts about other teams mantaining our code or just having 3rd parties having to deal with templates or context in spanish. Do you know of any best practice on this matter?

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• EF4 CTP5 - Map foreign key without object references?

  - by anon

  I feel like this should have a simple answer, but I can't find it. I have 2 POCOs: public class Category { public int Id { get; set; } public string Name { get; set; } } public class Product { public int Id { get; set; } public int CategoryId { get; set; } } Notice that there are no object references on either POCO. With Code-First, how do I make EF4 CTP5 define a relationship between the two database tables? (I know this is an unusual scenario, but I am exploring what's possible and what's not with Code-First)

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• MySql not storing foreign characters correctly

  - by acidzombie24

  On SQLITE this way fine. I switch to mysql and instead of ??? i get ???. The column is TEXT or sometimes VARCHAR(255) (i believe its VARCHAR(255) in this case). How do i have mysql save the characters properly?

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• Creating Two Cascading Foreign Keys Against Same Target Table/Col

  - by alram

  I have the following tables: user (userid int [pk], name varchar(50)) action (actionid int [pk], description nvarchar(50)) being referenced by another table that captures the relationship: <user1> <action>'s <user2>. I did this with the following table: userAction (userActionId int [pk], actionid int [fk: action.actionid], **userId1 int [fk ref's user.userid; on del/update cascade], userId2 int [fk ref's user.userid; on del/update cascade]**). However, when I try to save the userAction table i get an error because I have two cascading fk's against user.userid. Is there any way to remedy this or must I use a trigger?

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• New MySQL Cluster 7.3 Previews: Foreign Keys, NoSQL Node.js API and Auto-Tuned Clusters

  - by Mat Keep

  At this weeks MySQL Connect conference, Oracle previewed an exciting new wave of developments for MySQL Cluster, further extending its simplicity and flexibility by expanding the range of use-cases, adding new NoSQL options, and automating configuration. What’s new: Development Release 1: MySQL Cluster 7.3 with Foreign Keys Early Access “Labs” Preview: MySQL Cluster NoSQL API for Node.js Early Access “Labs” Preview: MySQL Cluster GUI-Based Auto-Installer In this blog, I'll introduce you to the features being previewed. Review the blogs listed below for more detail on each of the specific features discussed. Save the date!: A live webinar is scheduled for Thursday 25th October at 0900 Pacific Time / 1600UTC where we will discuss each of these enhancements in more detail. Registration will be open soon and published to the MySQL webinars page MySQL Cluster 7.3: Development Release 1 The first MySQL Cluster 7.3 Development Milestone Release (DMR) previews Foreign Keys, bringing powerful new functionality to MySQL Cluster while eliminating development complexity. Foreign Key support has been one of the most requested enhancements to MySQL Cluster – enabling users to simplify their data models and application logic – while extending the range of use-cases for both custom projects requiring referential integrity and packaged applications, such as eCommerce, CRM, CMS, etc. Implementation The Foreign Key functionality is implemented directly within the MySQL Cluster data nodes, allowing any client API accessing the cluster to benefit from them – whether they are SQL or one of the NoSQL interfaces (Memcached, C++, Java, JPA, HTTP/REST or the new Node.js API - discussed later.) The core referential actions defined in the SQL:2003 standard are implemented: CASCADE RESTRICT NO ACTION SET NULL In addition, the MySQL Cluster implementation supports the online adding and dropping of Foreign Keys, ensuring the Cluster continues to serve both read and write requests during the operation.  This represents a further enhancement to MySQL Cluster's support for on0line schema changes, ie adding and dropping indexes, adding columns, etc.  Read this blog for a demonstration of using Foreign Keys with MySQL Cluster.  Getting Started with MySQL Cluster 7.3 DMR1: Users can download either the source or binary and evaluate the MySQL Cluster 7.3 DMR with Foreign Keys now! (Select the Development Release tab). MySQL Cluster NoSQL API for Node.js Node.js is hot! In a little over 3 years, it has become one of the most popular environments for developing next generation web, cloud, mobile and social applications. Bringing JavaScript from the browser to the server, the design goal of Node.js is to build new real-time applications supporting millions of client connections, serviced by a single CPU core. Making it simple to further extend the flexibility and power of Node.js to the database layer, we are previewing the Node.js Javascript API for MySQL Cluster as an Early Access release, available for download now from http://labs.mysql.com/. Select the following build: MySQL-Cluster-NoSQL-Connector-for-Node-js Alternatively, you can clone the project at the MySQL GitHub page.  Implemented as a module for the V8 engine, the new API provides Node.js with a native, asynchronous JavaScript interface that can be used to both query and receive results sets directly from MySQL Cluster, without transformations to SQL. Figure 1: MySQL Cluster NoSQL API for Node.js enables end-to-end JavaScript development Rather than just presenting a simple interface to the database, the Node.js module integrates the MySQL Cluster native API library directly within the web application itself, enabling developers to seamlessly couple their high performance, distributed applications with a high performance, distributed, persistence layer delivering 99.999% availability. The new Node.js API joins a rich array of NoSQL interfaces available for MySQL Cluster. Whichever API is chosen for an application, SQL and NoSQL can be used concurrently across the same data set, providing the ultimate in developer flexibility.  Get started with MySQL Cluster NoSQL API for Node.js tutorial MySQL Cluster GUI-Based Auto-Installer Compatible with both MySQL Cluster 7.2 and 7.3, the Auto-Installer makes it simple for DevOps teams to quickly configure and provision highly optimized MySQL Cluster deployments – whether on-premise or in the cloud. Implemented with a standard HTML GUI and Python-based web server back-end, the Auto-Installer intelligently configures MySQL Cluster based on application requirements and auto-discovered hardware resources Figure 2: Automated Tuning and Configuration of MySQL Cluster Developed by the same engineering team responsible for the MySQL Cluster database, the installer provides standardized configurations that make it simple, quick and easy to build stable and high performance clustered environments. The auto-installer is previewed as an Early Access release, available for download now from http://labs.mysql.com/, by selecting the MySQL-Cluster-Auto-Installer build. You can read more about getting started with the MySQL Cluster auto-installer here. Watch the YouTube video for a demonstration of using the MySQL Cluster auto-installer Getting Started with MySQL Cluster If you are new to MySQL Cluster, the Getting Started guide will walk you through installing an evaluation cluster on a singe host (these guides reflect MySQL Cluster 7.2, but apply equally well to 7.3 and the Early Access previews). Or use the new MySQL Cluster Auto-Installer! Download the Guide to Scaling Web Databases with MySQL Cluster (to learn more about its architecture, design and ideal use-cases). Post any questions to the MySQL Cluster forum where our Engineering team and the MySQL Cluster community will attempt to assist you. Post any bugs you find to the MySQL bug tracking system (select MySQL Cluster from the Category drop-down menu) And if you have any feedback, please post them to the Comments section here or in the blogs referenced in this article. Summary MySQL Cluster 7.2 is the GA, production-ready release of MySQL Cluster. The first Development Release of MySQL Cluster 7.3 and the Early Access previews give you the opportunity to preview and evaluate future developments in the MySQL Cluster database, and we are very excited to be able to share that with you. Let us know how you get along with MySQL Cluster 7.3, and other features that you want to see in future releases, by using the comments of this blog.

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• SQL Server 2008: The columns in table do not match an existing primary key or unique constraint

  - by 109221793

  Hi guys, I need to make some changes to a SQL Server 2008 database. This requires the creation of a new table, and inserting a foreign key in the new table that references the Primary key of an already existing table. So I want to set up a relationship between my new tblTwo, which references the primary key of tblOne. However when I tried to do this (through SQL Server Management Studio) I got the following error: The columns in table 'tblOne' do not match an existing primary key or UNIQUE constraint I'm not really sure what this means, and I was wondering if there was any way around it?

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• Temporarily disabling foreign key constraints in SQL Server

  - by Renso

  Originally posted on: http://geekswithblogs.net/renso/archive/2013/06/24/temporarily-disabling-foreign-key-constraints-in-sql-server.aspxGoal: Is to temporarily disable all foreign key constraint and later enable the Constraint again?Solutions-- Disable all the constraint in databaseEXEC sp_msforeachtable "ALTER TABLE ? NOCHECK CONSTRAINT all"-- Enable all the constraint in databaseEXEC sp_msforeachtable "ALTER TABLE ? WITH CHECK CHECK CONSTRAINT all"

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• Stuck with foreign-architecture=i386 when using apt-get

  - by avilella

  I installed some packages a while ago and for some reason, they would only install with a special set of parameters that I used as recommended on a website (can't remember which one). Now, although harmless, I am stuck with these warnings every time I run apt-get: dpkg: warning: ignoring option --foreign-architecture=i386: this architecture cannot be foreign Any idea where is this lying around? How can I clean this up?

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• Django: many-to-one fields and data integrity

  - by John

  Let's say that I have a Person who runs an inventory system. Each Person has some Cars, and each Car has a very large number of Parts (thousands, let's say). A Person, Bob, uses a Django form to create a Car. Now, Bob goes to create some Parts. It is only at the form level that Django knows that the Parts belong to some specific Car, and that the Parts.ForeignKey(Car) field should only have a specific Car as a choice. When creating a Part, you have to mess with the form's constructor or similar in order to limit the choice of Cars to only the cars owned by Bob. It does not seem proper that to enforce this ownership at the form level. It seems that other users' Cars must be inaccessible to anyone but the owner of the Car. What do you all think about this, and is there any way to enforce this?

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• How do you handle descriptive database table names and their effect on foreign key names?

  - by Carvell Fenton

  Hello, I am working on a database schema, and am trying to make some decisions about table names. I like at least somewhat descriptive names, but then when I use suggested foreign key naming conventions, the result seems to get ridiculous. Consider this example: Suppose I have table session_subject_mark_item_info And it has a foreign key that references sessionSubjectID in the session_subjects table. Now when I create the foreign key name based on fk_[referencing_table]__[referenced_table]_[field_name] I end up with this maddness: fk_session_subject_mark_item_info__session_subjects_sessionSubjectID Would this type of a foreign key name cause me problems down the road, or is it quite common to see this? Also, how do the more experienced database designers out there handle the conflict between descriptive naming for readability vs. the long names that result? I am using MySQL and MySQL Workbench if that makes any difference. Thanks!

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• [Django] How to find out whether a model's column is a foreign key?

  - by codethief

  I'm dynamically storing information in the database depending on the request: // table, id and column are provided by the request table_obj = getattr(models, table) record = table_obj.objects.get(pk=id) setattr(record, column, request.POST['value']) The problem is that request.POST['value'] sometimes contains a foreign record's primary key (i.e. an integer) whereas Django expects the column's value to be an object of type ForeignModel: Cannot assign "u'122'": "ModelA.b" must be a "ModelB" instance. Now, is there an elegant way to dynamically check whether b is a column containing foreign keys and what model these keys are linked to? (So that I can load the foreign record by it's primary key and assign it to ModelA?) Or doesn't Django provide information like this to the programmer so I really have to get my hands dirty and use isinstance() on the foreign-key column?

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• NHibernate Pitfalls: Loading Foreign Key Properties

  - by Ricardo Peres

  This is part of a series of posts about NHibernate Pitfalls. See the entire collection here. When saving a new entity that has references to other entities (one to one, many to one), one has two options for setting their values: Load each of these references by calling ISession.Get and passing the foreign key; Load a proxy instead, by calling ISession.Load with the foreign key. So, what is the difference? Well, ISession.Get goes to the database and tries to retrieve the record with the given key, returning null if no record is found. ISession.Load, on the other hand, just returns a proxy to that record, without going to the database. This turns out to be a better option, because we really don’t need to retrieve the record – and all of its non-lazy properties and collections -, we just need its key. An example: 1: //going to the database 2: OrderDetail od = new OrderDetail(); 3: od.Product = session.Get<Product>(1); //a product is retrieved from the database 4: od.Order = session.Get<Order>(2); //an order is retrieved from the database 5:  6: session.Save(od); 7:  8: //creating in-memory proxies 9: OrderDetail od = new OrderDetail(); 10: od.Product = session.Load<Product>(1); //a proxy to a product is created 11: od.Order = session.Load<Order>(2); //a proxy to an order is created 12:  13: session.Save(od); So, if you just need to set a foreign key, use ISession.Load instead of ISession.Get.

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• How to delete a record when two tables have foreign key referenced to each other?

  - by vps

  Delete any record of them will report an error like this: ERROR 1451 (23000): Cannot delete or update a parent row: a foreign key constraint fails How to overcome this problem?

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• Foreign key restrictions -> yes or no?

  - by This is it

  I would like to hear some”real life experience” suggestions if foreign key restrictions are good or bad thing to enforce in DB. I would kindly ask students/beginners to refrain from jumping and answering quickly and without thinking. At the beginning of my career I thought that stupidest thing you can do is disregard the referential integrity. Today, after "few" projects I'm thinking different. Quite different. What do you think: Should we enforce foreign key restrictions or not? *Please explain your answer.

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