ApplyManyToMany

Configures a many-to-many relationship over an explicitly named join table, whose columns are named {TypeName}Id after the two entities, so an Account and a Tag give AccountId and TagId.

Both join columns are non-nullable, so EF Core cascades from either side by convention and a join row disappears with whichever entity it referenced.

Usage

AppDbContext.cs

using AlmightyShogun.EntityFrameworkCore.ModelBuilding;

modelBuilder.ApplyManyToMany<Account, Tag>(
    account => account.Tags,
    tag => tag.Accounts,
    "account_tags"
);

Entities.cs

public sealed class Account
{
    public int Id { get; set; }
    public List<Tag> Tags { get; set; } = [];
}

public sealed class Tag
{
    public int Id { get; set; }
    public required string Name { get; set; }
    public List<Account> Accounts { get; set; } = [];
}

WARNING

The join table carries nothing but the two keys, and its column names are fixed by the convention above. A join that stores data of its own, such as an EnrolledAt timestamp, or one that needs different column names, is past what this hides: configure it with UsingEntity directly.

Parameters

navigation: Expression<Func<TEntity, IEnumerable<TRelated>?>>
The collection property on TEntity, whose join column is named after that type.

inverseNavigation: Expression<Func<TRelated, IEnumerable<TEntity>?>>
The collection property on TRelated. This helper requires it because its parameter is not optional. EF Core itself supports a unidirectional many-to-many, which needs the fluent call written out instead.

joinTableName: string
The table holding the pairs. Named explicitly because EF Core's generated name concatenates the two entity names, which reads poorly in a migration and changes if either type is renamed.

Returns

The ModelBuilder instance with the relationship and its join table configured.

Type signature

public ModelBuilder ApplyManyToMany<TEntity, TRelated>(
    Expression<Func<TEntity, IEnumerable<TRelated>?>> navigation,
    Expression<Func<TRelated, IEnumerable<TEntity>?>> inverseNavigation,
    string joinTableName
) where TEntity : class where TRelated : class;