Overview

EF Core uses a metadata model to describe how the app’s entity types are mapped to the underlying database. Models are configured with:

Fluent API
Data annotations
Conventions

Conventions are not covered in these notes.

The above order describes the precedence EF Core takes when applying configuration.

Fluent API

Override the OnModelCreating method in the derived context and use fluent API to configure the model.

Fluent API configuration will override data annotations and conventions. The configuration is applied in the order the methods are called. The latest call will override previous calls.

using Microsoft.EntityFrameworkCore;

namespace SomeNamespace;

internal class SomeContext : DbContext
{
    public DbSet<Blog> Blogs { get; set; }

    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        modelBuilder.Entity<Blog>()
            .Property(b => b.Url)
            .IsRequired();
    }
}

public class Blog 
{
    public int BlogId { get; set; }
    public string Url { get; set; }
}

Using a separate class for an entity type

To reduce the size of OnModelCreating, configuration for an entity type can be factored out to a separate class:

public class BlogEntityTypeConfiguration : IEntityTypeConfiguration<Blog>
{
    public void Configure(EntityTypeBuilder<Blog> builder)
    {
        builder
            .Property(b => b.Url)
            .IsRequired();
    }
}

Then, in OnModelCreating, invoke Configure:

new BlogEntityTypeConfiguration().Configure(modelBuilder.Entity<Blog>());

EntityTypeConfiguration attribute

…

Data annotations

using System.ComponentModel.DataAnnotations;
using System.ComponentModel.DataAnnotations.Schema;
using Microsoft.EntityFrameworkCore;

namespace SomeNamespace;

internal class SomeContext : DbContext
{
    public DbSet<Blog> Blogs { get; set; }
}

[Table("Blogs")]
public class Blog 
{
    public int BlogId { get; set; }
    [Required]
    public string Url { get; set; }
}