Entity Framework query with simple join

Question

I am using Entity Framework 6 in a project and am having trouble creating a query.

Say my classes are defined like:

public class MyContext : DbContext
{
    public MyContext(string connectionString) : base(connectionString)
    {
    }

    public DbSet<EntityXXX> XXXSet { get; set; }
    public DbSet<EntityYYY> YYYSet { get; set; }
}


public class EntityXXX
{
    public string XXXName { get; set; }
    public int id { get; set; }
    public int YYYid { get; set; }
}

public class EntityYYY
{
    public string YYYName { get; set; }
    public int id { get; set; }
}

The YYYid property of EntityXXX is the 'id' of the EntityYYY instance that it relates to.

I want to be able to fill a Grid with rows where the first Column is XXXName and the second column is YYYName (from its related EntityYYY), but I can't see how to do this?

I'm sure it's really simple, but I'm new to EF.

MarkFl · Accepted Answer · 2018-02-09 15:06:13Z

2

You need to put a virtual navigation property on your EntityXXX

public virtual EntityYYY YYY { get; set; }

Then you can do a projection:

db.XXXSet
    .Select(x => new { x.XXXName, YYYName = x.YYY.YYYName })
    .ToList();

Which will get you the list you need.

answered Feb 9, 2018 at 15:06

MarkFl

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3 Comments

Cleve Over a year ago

Hi, thanks for your reply. I'm a bit confused why your solution doesn't refer to the id's at all? Can you explain please? I thought they would be involved somehow to make the match?

MarkFl Over a year ago

As long as you have it configured correctly, it knows that YYYid is the foreign key to the YYY table, thus the YYY property is the row from YYY that foreign key refers to. It's using the id in the background. If you were to look at the SQL produced it'd have a JOIN to the YYY table on the foreign key.

Cleve Over a year ago

Appreciate the additional comments - Thank you.

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