The picture show relation with two tables in my database;
Well as you can see there's a field called "DeviceTypeID" in the right side table.
Normally EF adds CompanyTypeID column to the ServiceLaburDefinitions model but it's disappeared last time I updated model from the database.
I am searching for a solution for a couple of hours but not able to find any solution. Could anyne suggest a solution?
Thanks.
ServiceLaburDefinitions is the depend entity and has the DeviceTypeID foreign key property defined.
So Entity Framework creates a navigation Key under the hood between the 2 tables based on DeviceTypeId key.
You can see for example how a navigation key is created also in the following example between the foreign key and the primary key
More information about navigation properties can be found here
When you create the model from the database, there is a checkbox marked "Include Foreign Key columns In The Model" - Make sure this is checked.
Related
I created a simple code first entity for learn purpose. Does EF6 automatically select the property to auto-increment? Because I found that it appears to be doing this. Does it automatically select the primary key too?
My search on this question yielded answers to questions of how to switch the identity property using "Data Annotations" Source but that doesn't exactly answer my question.
Does EF6 automatically select the property to auto-increment?
What you are describing is an Identity column (auto increments) which is also a primary key.
So let's visit the documentation:
Code First Data Annotations
Entity Framework relies on every entity having a key value that is
used for entity tracking. One convention of Code First is implicit key
properties; Code First will look for a property named “Id”, or a
combination of class name and “Id”, such as “BlogId”. This property
will map to a primary key column in the database.
Note : the key will also be defined as Identity by default
There is a lot more to this and various ways to configure fields and tables, so I recommend reading the documentation thoroughly.
I use code first of Entity framework. There are two classes "Question" and "User". I defined a relationship as below:
this.HasRequired(v => v.Creator).WithMany(v => v.Questiones)
.HasForeignKey(v => v.CreatorId).WillCascadeOnDelete(false);
After gernerating the database I found that it always create foreign key between Id of User and CreatorId of Question. Because of lower performance of FK(and other reason),I want to define navigation property relationship without setting foreign key in database? Delete FK after EF created it?
If cannot do this using fluent api, could you tell me why EF designed in this way please?
About the lower performance of FK. I have a User table with 5 Million records in it. when I insert a Question into db, since the db check the question.CreatorId validation from User table, it always slower than without FK.
And there are many other reasons that I need to remove FK.
I think I am somewhat obsession because I think that deleting FK after created it is strangely and ugly. What i want is implementing this by using something like WithoutForeignKey in fluent api:
this.HasRequired(v => v.Creator).WithMany(v => v.Questiones)
.WithoutForeignKey(v => v.CreatorId).WillCascadeOnDelete(false);
Without questioning why are you trying to do this strange thing and going just to the answer: you could delete fk constraint after generated, or you could use migrations and remove FK generation from the migration code.
SQL code generated when traversing nav properties will work even if fk constraint doesn't exist, except for cascade deleting
If you want a relationship between two tables, you need to define a foreign key. No way around it. Even if you use Map() in fluent api, you can only hide the foreign key in your model, in the background EF will still use it and it will exist in the database.
Also I don't get what you mean by "performance" of foreign key? One extra (likely small) column won't make a difference. If you mean the navigation properties for the performance part, you can do 3 things:
Don't include them in your model
Make them non-virtual to disable lazy loading
Disable lazy loading all together with ctx.Configuration.LazyLoadingEnabled = false;
If you don't want to tell db about relation and treat both entities as not related (I wonder why), then just ignore these navigation properties and FK field. Note that you will be responsible for managing related entities: saving and loading them from db, updating ids etc
this.Ignore(q => q.Creator);
this.Ignore(q => q.CreatorId);
And you also need to ignore other side of relation, otherwise EF will generate FK column with default name Creator_CreatorId. So in Creator entity configuration:
this.Ignore(c => c.Questiones);
Scenario:
Database first.
I have a table with no primary key set and I'm trying to make an update with Entity Framework.
This is the error message I keep getting:
The property 'inactive_date' is part of the object's key information and cannot be modified.
If I set the fields 'Entity Key' value to 'false' I get this error messge:
Modifications to tables where a primary key column has property 'StoreGeneratedPattern' set to 'Computed' are not supported. Use 'Identity' pattern instead. Key column: 'timestamp'. Table: 'plat12Model.Store.glchart'.
Would this be corrected if I created a primary key? Can I set a primary key in my code rather than on the database?
By default, EF will make tables without primary keys and views into read-only classes where every field is part of the composite key. You can modify the conceptual model to reflect the actual behavior as long as you retain a key value that EF will use for object tracking. As the error message states, you also need to make the columns no longer computed in order to update them as well.
I have an authors -> authorsbooks <- books in my database. I created an entity data model from this and I noticed that the association entity didn't show up in the model(I think it's inferred).
I want to drag 2 EntityDataSources onto the designer, a gridview of authors, and when a user clicks to select an author another gridview below will show all the books assoiciated with that author.
How do I configure that second entitydatasource because when I try to configure it I don't see the authorsbooks association entity in the entitysetname dropdownlist. I'm thinking to set this as the datasource to the books gridview? Am I misunderstanding something?
Thanks,
rodchar
Entity Framework will infer the relationships based on the Foreign Keys in your database.
Does your AuthorBooks table have a foreign key to the Author table?
Also, when you add your tables onto your EDMX, make sure you tick "Include Foreign Keys in Model".
If done correctly, when you type Author., you should see AuthorBooks as an EntitySet.
Pardon the massive headline.
I'm in the situation of having to build an application on top of a database, that I cannot make any changes to. The database does not have any primary- or foreignkeys set.
I'm using linq-2-sql, and I'm interested in having some properties exposed on the entities generated from my dbml. For instance, in the hypothetical example of a one-to-many relationship between table education and student - where each student record has a reference to an education id, I'd like to be able to go:
var student = GetAStudentFromContextOrWhatever();
var studentsEducation = student.Education;
It is my experience, that this kind of property is automatically generated when I drag'n'drop tables with foreignkey relationships from the server explorer.
However as previously mentioned, in this case I do not have these foreign key relationships - rather I am adding the relationships manually in the dbml file, specifying parent and child class.
When I add these relationships, I expect the involved entities in the designer.cs of my context to get populated with properties of a kind like those described above.
This, however, does not happen.
What must I do for my dbml to create these properties for me - based on these manually mapped associations between entities/tables that, on a database level, do not have foreign key associations?
Cheers!
L2S is just that Linq-to-SQL. If it isn't in SQL it won't be generated. The expression trees behind L2S just can't understand what you are doing. The place for your association is in a partial class file which you will have create manually. Also it probably won't update or insert through the association.
I know this is a very old question, but I just ran into the same problem. In order for the relationship in the DBML designer to automatically create the association properties for you, you need to have primary keys on your objects. If you click the column name in the designer, you'll see that your PK field has PrimaryKey = false. Switch that to True and build; all should be well.
Patrick