Entity Framework multiple mapping to same table DB first

Question

I have an issue with an Entity Framework from DB model.

My issue is down to the fact that one of my models has a multiple references to one table.

public partial class Customer
{
    public int Id { get; set; }

    public Nullable<int> PrimaryEngId { get; set; }
    public Nullable<int> AssignedDevloperId { get; set; }

    public virtual Engineer Engineer { get; set; }
    public virtual Engineer Engineer1 { get; set; }
}

In my model the columns are mapped respectively, however when a colleague builds the model from the same database the two are reversed.

I believe the issue is that the first mapping to in was the primaryEngId and the Db constraint is called FK_Customer_Engineer.

And the assigned developer id was added subsequently and the DB constraint is called FK_Customer_Devloper

So alphabetically Developer come before Engineer and Entity Framework now maps them the other way round.

My code references the Engineer in quite a lot of places which now won't work

Is there any way out of this?

Many thanks

Ian

vittore · Accepted Answer · 2016-03-14 13:01:36Z

2

You have to add missing ForeignKey attributes on foreign keys for those two navigation properties:

[ForeignKey("Primary")]
public int? PrimaryEngId { get; set; }

[ForeignKey("Assigned")]    
public int? AssignedDevloperId { get; set; }

public virtual Engineer Primary { get; set; }

public virtual Engineer Assigned { get; set; }

NOTE: Also don't use generic names for navigation properties with EF. In the nutshell one of the best things EF gives you is that you can say:

@myCustomer.Assigned.Name

etc in the view, and you are totally screwing it up with names like Engineer and Engineer1.

NOTE2: Keep Nullable<int> to code generation. int? is a lot more readable.

NOTE3: Use VS refactoring to rename properties Engineer and Engineer1 to what they should be ( PrimaryEngineer and AssignedEningeer etc). After that add ForeignKey attributes to your model. That should be enough. However, any future changes that you are doing has to be done in the Code and not in db.

IF on the other hand you are constantly regenerating entities and context code from database, make sure that all your foreign keys has meaningful names, as EF will use them to generate name.(ie it is not named Engineer1 out of blue) Rename those foreign keys to reflect what logical relationship is. Ie you most likely have the following foreign keys in db:

 FK_Customer_Engineer

 FK_Customer_Engineer1

You need to rename them to

 FK_Customer_PrimaryEngineer

 FK_Customer_AssignedEngineer

Update: you can have different column name and property name like so:

[Column("PrimaryEngId")]
[ForeignKey("Primary")]
public int? PrimaryID { get; set; }

edited Mar 14, 2016 at 13:01

answered Mar 14, 2016 at 12:32

vittore

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2 Comments

Ian Over a year ago

Sadly when I took over as the project Lead the Model is being developed using the DB first system. so the DB code for all this is generated by entity Framework, is there issues with changing the code in the DB first system?

vittore Over a year ago

Depends on where you are planing to do changes to the schema - in the code or in the schema. If you need to regenerate classess from db every tme it does not make much sense to change it, as you will end up doing it every time. If you are making any future change in the code and run ef-migration on db, you can update those, because as far as EF is concerned of only Foreign Key name, which is by default is equal to property name, but can be overriden with attribute, if you want your code to follow your code conventions /style guides etc.

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