Question

Using a code-first approach I’d like to map a single model to multiple table names dynamically. Currently I can do something like modelBuilder.Entity(Of Person)().MapSingleType().ToTable("Managers") but as the OnModelCreating method is only called once I can’t map it to other table names on the fly.

In our current LinqToSql version we’re overriding the MetaModel.GetTable() and returning a new TableAttribute with our dynamic name. I haven’t found an attribute like that in EF (even if there were I wouldn’t know how to override that yet). So my question is: Is it possible to do this (yet)?

Update

I’ve found that I can prevent the OnModelCreating method from caching the mappings by calling

modelBuilder.CacheForContextType = false;

As a result I can assign table definitions on instantiation of the object. This isn’t quite how I wanted to do it but it works.

Update

Oh boy, was the above a big mistake…Caching exists for a reason! 🙂 So I’m back to square one with POCO object mapping. I’ll post an update if I figure out a solution.

Final

Incase anybody cares how I’ve currently solved this issue, here you go:

First I created a separate library with the POCO tables and an Interface

public interface IDataContext {
    System.Data.Entity.DbSet<TableGeneric> TableGeneric { get; set; }

    int SaveChanges();
}


public class TableGeneric {
    [Key]
    public int Column1 { get; set; }
    public string Column2 { get; set; }
    public DateTime Column3 { get; set; }
    public string Column4 { get; set; }
    public string Column5 { get; set; }
}

Then, using the CSharpCodeProvider I created a class that takes the following template and turns it into a type definition:

class DataContext : System.Data.Entity.DbContext, IDataContext {
    public System.Data.Entity.DbSet<TableGeneric> TableGeneric { get; set; }

    protected override void OnModelCreating(ModelBuilder modelBuilder) {
        modelBuilder
            .Entity<ContextTesting.Interfaces.EF.TableGeneric()
                .MapSingleType()
                .ToTable("$TableName$");
    }
}

With the generated type I’m able to create an instance so here we go

Type typeAccountants = BuildContext.CreateGenericTable("Accountants");
IDataContext context = (IDataContext)Activator.CreateInstance(typeAccountants);

Then the rest is just as if you had a normal DataContext. Hope this helps someone else.

Answer 1

Incase anybody cares how I’ve currently solved this issue, here you go:

First I created a separate library with the POCO tables and an Interface

public interface IDataContext {
    System.Data.Entity.DbSet<TableGeneric> TableGeneric { get; set; }

    int SaveChanges();
}


public class TableGeneric {
    [Key]
    public int Column1 { get; set; }
    public string Column2 { get; set; }
    public DateTime Column3 { get; set; }
    public string Column4 { get; set; }
    public string Column5 { get; set; }
}

Then, using the CSharpCodeProvider I created a class that takes the following template and turns it into a type definition:

class DataContext : System.Data.Entity.DbContext, IDataContext {
    public System.Data.Entity.DbSet<TableGeneric> TableGeneric { get; set; }

    protected override void OnModelCreating(ModelBuilder modelBuilder) {
        modelBuilder
            .Entity<ContextTesting.Interfaces.EF.TableGeneric()
                .MapSingleType()
                .ToTable("$TableName$");
    }
}

With the generated type I’m able to create an instance so here we go

Type typeAccountants = BuildContext.CreateGenericTable("Accountants");
IDataContext context = (IDataContext)Activator.CreateInstance(typeAccountants);

Then the rest is just as if you had a normal DataContext. Hope this helps someone else.