How to implement IModelCacheKeyFactory in EF Core

Question

The story: in our multi-tenant app (one PostgreSql db, multiple schemas) we need to use one DbContext against multiple schemas.

What I tried: holding a cache (Dictio

Answer 1

There actually have demo project in docs https://github.com/aspnet/EntityFramework.Docs/tree/master/samples/core/DynamicModel adding post for convinience !

Answer 2

Here is an example.

Derived DbContext that replaces it's ModelCacheKey (and factory) with a Custom one.

class MyDbContext : DbContext
{
    public MyDbContext(string schema)
    {
        Schema = schema;
    }

    public string Schema { get; }

    protected override void OnConfiguring(DbContextOptionsBuilder options)
        => options
            .UseSqlServer("...")
            .ReplaceService<IModelCacheKeyFactory, MyModelCacheKeyFactory>();

    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        modelBuilder.HasDefaultSchema(Schema);

        // ...
    }
}

The factory that creates the Context with a specific key.

class MyModelCacheKeyFactory : IModelCacheKeyFactory
{
    public object Create(DbContext context)
        => new MyModelCacheKey(context);
}

The custom ModelCacheKey per context.

class MyModelCacheKey : ModelCacheKey
{
    string _schema;

    public MyModelCacheKey(DbContext context)
        : base(context)
    {
        _schema = (context as MyDbContext)?.Schema;
    }

    protected override bool Equals(ModelCacheKey other)
        => base.Equals(other)
            && (other as MyModelCacheKey)?._schema == _schema;

    public override int GetHashCode()
    {
        var hashCode = base.GetHashCode() * 397;
        if (_schema != null)
        {
            hashCode ^= _schema.GetHashCode();
        }

        return hashCode;
    }
}