Cross database querying in EF

No, you can't. You will have to create to contexts and do the joining your self. See here.

You could resolve to database trickery, creating a view in one database the reflects a table in the other one.

EF context does not support cross database queries. You need to expose posts in database1 through SQL View (or synonym) and use it as part of that database.

You can use ExecuteStoreQuery, like:

var myOb = context.ExecuteStoreQuery<PlainOldClrObject>(
        @"select  * 
          from    db1.dbo.table1 t1
          join    db2.dbo.table2 t2
          on      t2.t1_id = t1.id
          where   t1.id  = {0}",
        table1Id).FirstOrDefault();

You'd have to define a PlainOldClrObject class with the columns as properties with getters/setters, like:

class PlainOldClrObject
{
    public int Id ( get; set; }
    public int Name ( get; set; }
    ...
}

I know this is an old question, but this is actually possible. If the databases are on the same server, then all you need to do is use a DbCommandInterceptor.

As an example, if I attach a DbCommandInterceptor to MyContext, I can intercept all command executions and replace the specified table(s) in the query with my full-db paths.

public override void ReaderExecuting(DbCommand command, DbCommandInterceptionContext<DbDataReader> interceptionContext)
{
    // Here, I can just replace the CommandText on the DbCommand - but remember I
    // want to only do it on MyContext
    var context = contexts.FirstOrDefault() as MyContext;
    if (context != null)
    {
        command.CommandText = command.CommandText
            .Replace("[dbo].[ReplaceMe1]", "[Database1].[dbo].[Customers]")
            .Replace("[dbo].[ReplaceMe2]", "[Database2].[dbo].[Addresses]")
            .Replace("[dbo].[ReplaceMe3]", "[Database3].[dbo].[Sales]");
    }

    base.ReaderExecuting(command, interceptionContext);
}

The nice thing also about this approach is that the EF Model Mapping still works properly and respects column attributes, requires no views, and requires no stored procedures.