I'm using LINQ expressions in order to build select and where expressions dynamically.
The select method looks like this:
public Expression<Func<TSource, TTarget>> GetSelectExpression<TSource, TTarget>()
{
ParameterExpression l_pe = Expression.Parameter(Base_type, "source");
...
Expression<Func<TSource, TTarget>> l_return = Expression.Lambda<Func<TSource, TTarget>>(l_select, new ParameterExpression[] { l_pe });
l_return.Compile();
return l_return;
}
The Where method looks like the following:
public Expression<Func<TTarget, bool>> GetWhereExpression<TTarget>()
{
ParameterExpression l_pe = Expression.Parameter(Dto_type, "dto");
....
Expression<Func<TTarget, bool>> l_return = Expression.Lambda<Func<TTarget, bool>>(l_or, new ParameterExpression[] { l_pe });
l_return.Compile();
return l_return;
}
If I call the following statements, everything works fine:
var l_where = GetWhereExpression<CrudChangetaskDto>();
var l_select = GetSelectExpression<A_Changetask, CrudChangetaskDto>();
IQueryable<CrudChangetaskDto> l_query = l_db.A_Changetask.Select(l_select).Where(l_where);
var lt_result = l_query.ToList();
Because of using the WHERE and SELECT methods more dynamically, I like to have a method returning an IQueryable like the following (PaltrConnect is the database context):
IQueryable<TTarget> GetSearchhelpvalue<TSource, TTarget>(PaltrConnect context)
{
var l_dbset = context.Set(typeof(TSource));
IQueryable<TTarget> l_query = l_dbset.Select(GetSelectExpression<TSource,TTarget>()).Where(GetWhereExpression<TTarget>());
return l_query;
}
Unfortunately, this is syntactically not correct. I get the error message System.Linq.IQueryable cannot be converted into System.Linq.IQueryable.
Finally, I like to call GetSearchhelpvalue in the following way:
using (var l_db = new PaltrConnect)
{
IQueryable<CrudChangeTaskDto> l_query = GetSearchhelpvalue<A_Changetask, CrudChangetaskDto>(l_db);
var lt_result = l_query.ToList();
}
How can I access the DbSet of the type which corresponds to TSource or how can this be solved?
Yours Stephan