I have two tables A and B in my db with a foreign key between both. Table A has a PrimaryKey and UniqueKey. Table B is referencing Table A by using the UniqueKey. If I generate the ef model from the database then no association between A and B is generated and I couldn't find a way to manually add the association. However, Linq2Sql recognizes the relationship as expected.
Any ideas?
See this MSDN blog post: http://blogs.msdn.com/b/efdesign/archive/2011/03/09/unique-constraints-in-the-entity-framework.aspx. In brief, this isn't supported in V4, though the EF team seems to have plans to support it in future releases.
Related
I have 2 entities in my domain that have a one-to-one relationship with one another.
Entity Business has a Promotion. And Promotion has a Business. I know this doesn't make a lot of sense and I could as well integrate the fields of Promotion into my Business entity, but I'm dealing with a legacy database here and I'm trying to model my domain on top of it without changing anything in the database for now.
My problem is that although the relationship goes both ways, it's only stored on the side of the promotion table that has a business_id foreign key, but there is no promotion_id foreign key in the business table. So when I try to run my app, Grails can't find the promotion_id column it expects to find for the promotion field in Business.
Is there any way to model my domain entity so that it understands that the column for the relationship is in the destination table only?
Right after I asked this question, I found my own answer: using hasOne as explained in http://grails.org/doc/latest/ref/Domain%20Classes/hasOne.html
I'm using Entity Framework 4 and with a Database First binding, and EF is not generating the entities for a few of my tables. I'm not getting any errors, and no matter how many times I select the tables to generate from the "Update Model from Database" popup menu on the design surface, the same tables are still missing from the model.
I get no errors in the wizard. They just don't get generated. Any clues?
EF requires a primary key on the table. EF will not map tables for which it can't find or derive a primary key. If all columns are nullable, it can't assume a primary key. If one or more columns are not nullable, EF will evidently derive a primary key for the table.
EF will ignore table without primary keys.
Options I can think of:
Did you check the box next to those tables?
Did you previously add them, then delete their entities but keep the cache of the tables?
If so you can remove them from entity browser window and re-add them
or manually add entities and define the table they map to in mappings window.
Perhaps tables were classified as relations instead of entities?
You can manually add the entities and choose the table they map to in mappings window.
Actually, in my case, it doesn't work because I was using a hierarchyid field as a primary key and EF doesn't work with this field type, so, it didn't import the table, because a valid PK is required.
A possibility is when you're using tables with some different field types, as hierarchy in SQL Server.
Without Primary Key Tables where Skip Automatically on EF, OtherWise You Fix a Value as Not Null.
I'm an NHibernate developer trying to give Entity Framework a shot in a hobby project. I'm used to specifying mapping data in code using Fluent NHibernate. Pardoning Microsoft's belief that developers shouldn't be allowed to write code, I'm trying to create my mappings using the Entity Framework's visual designer surface (which you get by opening the .edmx file in Visual Studio).
I have no idea how to set up a many-to-many relationship! I have 'updated the model' from the database, but I get two one-to-many relationships with a new entity corresponding to the junction table (which contains only foreign keys and its own primary key).
So far, all attempts at working this out by clicking on the entities and relationships and such have failed. Can anyone give me a pointer?
Your junction table must be what MS calls a 'pure join table' - it must contain only the two foreign keys, and no other columns. In your case, that means you must delete the primary key column.
When you add the association to the model you choose each of your two tables and choose "many" on both sides of the relationship. When this generates the database script a join table with only the two keys will be created for you.
By the way: If you don't like using Model-first and would rather code research "Code-First" development for the Entity Framework. You can also do Database-First if you prefer that.
I'm using EF 4.0 and was able to create self referencing many to many relationship. Person and family members. What I also want is to add additional attribute like 'mother', 'brother', 'sister' for each relationship. At the database level, this model generates two tables. Person and PersonRelationship. PersonRelationship table has person_id, and relative_id as PK. I like to have another column relationshiptype in PersonRelationship table and reference in EF 4.0. Please let me know how to do it if you don't mind?
If I were you I would create a table "RelationshipTypes". It holds the different possible types of relationship for you. Just two columns ID and Name of relationship.
Second you just add the RelationshipTypeID to your PersonRelationship and mark it as primary key too.
You should have then three primary keys in your table. Just update your model in Visual Studio and it should work.
Does this help?
Regards Thomas
I am just getting started with Microsoft's Entity Framework, using it for an MVC project since MS seems to be really pushing it, and I'm running into some issues. In my database there are multiple lookup tables tied to a single table via foreign keys. Within the entity framework I am trying to combine these into one so that I have a simplified single view for this data in my model. However, this doesn't seem possible from the designer view. Is there something obvious I'm missing? Is there a way that I can edit the edmx file manually to produce this sort of model?
At the moment, Foreign keys and lookup tables in Entity Framework are a PAIN.
EF with LINQ makes getting your data super-easy, and on the surface it looks easy to update, but with lookup tables things get difficult (for now... read on...)
I'm not sure how you would "combine" your lookup tables into a single table. If each table contains a different type of "lookup entity" then IMHO they should be represented separately in your EDM. I'm guessing you're having headaches updating a record's foreign keys to the lookup tables. That's because it is a headache.
Changing foreign key values:
MyDBEntities _db = new MyDBEntities();
//get a Person
MyDBEntities.Person person = (from p in _db.Persons
where p.Id = 1
select p).First();
// This sets the foreign key value in the Person table on the PersonType field
person.PersonTypeReference = new EntityKey("MyDBEntities.PersonType", "PersonTypeId", 3)
The next release version of the Entity Framework will have a new concept called "FK Associations." This will bring back the sanity of setting the foreign key value directly rather than having to create and set an EntityKey.
HTH.