实体框架和在单个上下文中具有多个模式的迁移

Question

I am developing a multi-tenant application with Entity Framework Code First. Each tenant will have a different schema in the database, but the application will have a single Context and model for all tenants.

The Entity Framwork 6 is able to use multiple schemas with multiple contexts in the same database, but I didn't find a way to use multiple schemas with a single Context.

I have generated migrations (by command line) to the default “dbo” schema. I would like to update other schemas using these migrations.

Answer 1

While I agree that multiple context is absolutely the better way to go (and is how I have my own projects setup), I wanted to answer your original question of how to use multiple schemas in a single context:

Inside of your mapping configuration for each model you can call 'ToTable(myTableName, mySchema)' to modify the schema to which a table belongs:

public class MyEntityMap : EntityTypeConfiguration<MyEntity>
{
    public MyEntityMap ()
    {
        HasKey(t => t.MyId);
        Property(t => t.MyId)
            .HasDatabaseGeneratedOption(DatabaseGeneratedOption.Identity);

        ToTable("MyEntity", "MySchema");
    }
}

This will allow you to set the schema for each table separately while maintaining a single context.

Since you stated that you want to use the same model in different schemas that makes it a little more difficult without knowing more about your setup. If you are dealing only with a handful of customers and don't mind maintaining their schemas in code then you can simply create a map for each schema (as above) and then add a new DbSet for each customer. If you are trying to make this scalable up to a large number of customers then I would highly suggest looking into a different approach because your dba might scream when he sees 100+ identical tables in different schemas as opposed to using a customerID column on each table.

Answer 2

Looking at these posts

http://thedatafarm.com/data-access/digging-in-to-multi-tenant-migrations-with-ef6-alpha/

http://romiller.com/2011/05/23/ef-4-1-multi-tenant-with-code-first/

I came up with this context

public class DataLayerBuilder : DbContext
{
    private static  string conStr = string.Empty ;
    private DataLayerBuilder(DbConnection connection, DbCompiledModel model)
    : base(connection, model, contextOwnsConnection: false){ }
    public DbSet<Person> People { get; set; }

    private static ConcurrentDictionary<Tuple<string, string>, DbCompiledModel> modelCache
        = new ConcurrentDictionary<Tuple<string, string>, DbCompiledModel>();

    /// <summary>
    /// Creates a context that will access the specified tenant
    /// </summary>
    public static DataLayerBuilder Create(string tenantSchema)
    {
        conStr = ConfigurationManager.ConnectionStrings["ConnSTRName"].ConnectionString;
        var connection = new SqlConnection(conStr);
        var compiledModel = modelCache.GetOrAdd(
            Tuple.Create(conStr, tenantSchema),
            t =>
            {

                var builder = new DbModelBuilder();
                builder.HasDefaultSchema(tenantSchema);
                builder.Entity<Person>().ToTable("People");                   
                builder.Entity<Contact>().ToTable("Contacts");
                var model = builder.Build(connection);
                return model.Compile();
            });

        return new DataLayerBuilder(connection, compiledModel);
    }

    /// <summary>
    /// Creates the database and/or tables for a new tenant
    /// </summary>
    public static void ProvisionTenant(string tenantSchema)
    {
        try
        {
            using (var ctx = Create(tenantSchema))
            {
                if (!ctx.Database.Exists())
                {
                    ctx.Database.Create();
                }
                else
                {
                    ctx.Database.Initialize(true);

                }
            }
        }
        catch (Exception)
        {

            throw;
        }
    }
}

So far I've been able to add Multiple Tenants Using the following Code

 public void ProvisionTest()
    {
        //Arrange
        var tenant = "test2";

        //Act
        DataLayerBuilder.ProvisionTenant(tenant);

    }
}

Improving upon the above code I think you can write a simple Function to update your table structures for each user

I hope this helps

Answer 3

The solution is probably best seen as a combination of both Robert Petz and alfkonne answers with a few more tools around connection management and migration management. I prefer DB level not schema per Customer for customer specific backup purposes. You can do schema specific backup/restore IF setup properly. But make sure any external tools involved deal with schema based restore.

Answer 4

You can use multiple schemes in a single context. In each of the entities or class you must add the following Data Annotations:

[Table("TableName", Shema = "ShemaName")]

public class Entity
{

}