How to specify a composite primary key using EFCore Code First Migrations

Question

I'm using Asp.Net Core 2.1, Mvc, c#, EF Core with Code First and Migrations.

I'm trying to build a table that has a composite primary key in the Migration.Up() method:

migrationBuilder.CreateTable(
    name: "TagValueAttributes",
    columns: table => new {
        TagValueID = table.Column<Int64>(nullable: false),
        Identifier = table.Column<string>(nullable: false, unicode: true, maxLength: 256),
        Value = table.Column<string>(nullable: true, unicode: true, maxLength: 2048)
    },
    constraints: table => {
        table.PrimaryKey(
            name: "PK_TagValueAttributes",
            columns: // what goes here???
        )
    }
);

I don't know what to specify for the columns parameter of the constraints table.PrimaryKey() call. I would like columns TagValueID, and Identifier to form the composite key.

What do I need to specify for the columns parameter?

Emlen

Answer 1

Why do you want to put this in the Migration.Up() method ?

You can do this via the Fluent API in your DbContext by overriding OnModelCreating() method :

protected override void OnModelCreating(ModelBuilder builder)
{
    builder.Entity<TagValueAttributes>().HasKey(t => new { t.TagValueID, t.Identifier });
}

If you want tho keep this in Migration.Up() then do:

table.PrimaryKey(
    name: "PK_TagValueAttributes",
    columns: t => new { t.Identifier, t.TagValueID }
);

Siegler

Thanks for your comments. However, there does not appear to be a property of table called TagValueID not one called Identifier. – Emlen

I want this in Migration.Up() because I'm using migrations. If I put it in DbContext.OnModelCreating() then I don't get to use Migrations. – Emlen

Mmmmh okay I removed this part of the answer, I'll be back to you in minutes with a solution I hope. – Siegler

You were very close. I'm going to fix your answer and accept it. – Emlen

Found the solution on my side a few seconds ago. Glad your problem was solved have a nice day. – Siegler

Answer 2

Using EF Core 7.0 you can use data annotations
https://learn.microsoft.com/en-us/ef/core/modeling/keys?tabs=data-annotations

using Microsoft.EntityFrameworkCore;

[PrimaryKey(nameof(Identifier), nameof(TagValueID))]
internal class table
{
    public Int64 Identifier { get; set; }
    public string TagValueID { get; set; }
    public string Value { get; set; }
}

Intervalometer

PrimaryKey is under which name space? PrimaryKeyAttribute could not be found error is throwing even using System.ComponentModel.DataAnnotations and System.ComponentModel.DataAnnotations.Schema – Require

@ZinMin, the only namespace I am using is Microsoft.EntityFrameworkCore. Again, Microsoft introduced the PrimaryKey attribute in EF Core 7.0 (learn.microsoft.com/en-us/ef/core/modeling/…) – Intervalometer

@ZinMin Took me a moment time to find it, but you have to install the Microsoft.EntityFrameworkCore.Abstractions package to use it. – Othaothe