How to change database schema on runtime in EF7 or EF core - entity-framework

Question

My database have different schema depending on user selections on runtime.
My code is below:
public partial class FashionContext : DbContext
{
private string _schema;
public FashionContext(string schema) : base()
{
_schema = schema;
}
public virtual DbSet<Style> Styles { get; set; }
protected override void OnConfiguring(DbContextOptionsBuilder options)
{
options.UseSqlServer(#"Server=.\sqlexpress;Database=inforfashionplm;Trusted_Connection=True;");
}
protected override void OnModelCreating(ModelBuilder modelBuilder)
{
modelBuilder.Entity<Style>()
.ToTable("Style", schema: _schema);
}
}
Upon testing. I created a context instance with 'schema1'.
So far so good.
But when I create another context instance with different schema 'schema2', the resulting data in which the schema is still on 'schema1'.
Here is the implementation:
using (var db = new FashionContext("schema1"))
{
foreach (var style in db.Styles)
{
Console.WriteLine(style.Name);
}
}
Console.ReadLine();
Console.Clear();
using (var db = new FashionContext("schema2"))
{
foreach (var style in db.Styles)
{
Console.WriteLine(style.Name);
}
}
Console.ReadLine();
Later I noticed that the OnModelCreating is called only one time, so it is never called again when you create a new context instance of the same connection string.
Is it possible to have dynamic schema on runtime? Note: this is possible in EF6

Answer 1

One of possible way was mentioned above, but briefly, so I will try to explain with examples.
You ought to override default ModelCacheKeyFactory and ModelCacheKey.
ModelCachekeyFactory.cs
internal sealed class CustomModelCacheKeyFactory<TContext> : ModelCacheKeyFactory
where TContext : TenantDbContext<TContext>
{
public override object Create(DbContext context)
{
return new CustomModelCacheKey<TContext>(context);
}
public CustomModelCacheKeyFactory([NotNull] ModelCacheKeyFactoryDependencies dependencies) : base(dependencies)
{
}
}
ModelCacheKey.cs, please review Equals and GetHashCode overridden methods, they are not best one and should be improved.
internal sealed class ModelCacheKey<TContext> : ModelCacheKey where TContext : TenantDbContext<TContext>
{
private readonly string _schema;
public ModelCacheKey(DbContext context) : base(context)
{
_schema = (context as TContext)?.Schema;
}
protected override bool Equals(ModelCacheKey other)
{
return base.Equals(other) && (other as ModelCacheKey<TContext>)?._schema == _schema;
}
public override int GetHashCode()
{
var hashCode = base.GetHashCode();
if (_schema != null)
{
hashCode ^= _schema.GetHashCode();
}
return hashCode;
}
}
Register in DI.
builder.UseSqlServer(dbConfiguration.Connection)
.ReplaceService<IModelCacheKeyFactory, CustomModelCacheKeyFactory<CustomContext>>();
Context sample.
public sealed class CustomContext : TenantDbContext<CustomContext>
{
public CustomContext(DbContextOptions<CustomContext> options, string schema) : base(options, schema)
{
}
}

Answer 2

You can build the model externally and pass it into the DbContext using DbContextOptionsBuilder.UseModel()
Another (more advanced) alternative is to replace the IModelCacheKeyFactory to take schema into account.

Answer 3

I found a way to recreate the compiled model on each context creation.
public partial class MyModel : DbContext {
private static DbConnection _connection
{
get
{
//return a new db connection
}
}
private static DbCompiledModel _model
{
get
{
return CreateModel("schema name");
}
}
public MyModel()
: base(_connection, _model, false)
{
}
private static DbCompiledModel CreateModel(string schema)
{
var modelBuilder = new DbModelBuilder();
modelBuilder.HasDefaultSchema(schema);
modelBuilder.Entity<entity1>().ToTable(schema + ".entity1");
var builtModel = modelBuilder.Build(_connection);
return builtModel.Compile();
}
}