LINQ to Entities does not recognize the method 'System.Collections.Generic.Dictionary`2[System.Int32,System.String] ToDictionary

Question

I am trying to retrieve list of EmployeeDTO from DB which are stored in Employee table. Every employee can have one or more specialty. Specialty are stored in OrganizationSpecialtyType . Employee and OrganizationSpecialtyType are related with "many-to-many" via EmployeeSpecialty table.

I'm using the following query for that, and got an exception like in title:

var q = _context.Employee.Where(p => employeeEMIIDs.Contains(p.EmployeeID))
            .Select(p => new EmployeeDTO
                                    {
                                        EmployeeID = p.EmployeeID,
                                        GenderTypeID = p.GenderTypeID,
                                        FirstName = p.FirstName,
                                        LastName = p.LastName,
                                        Name = p.Name,
                                        MiddleName = p.MiddleName,
                                        DOB = p.DOB,
                                        Suffix = p.Suffix,
                                        Title = p.Title,
                                        Specialty = p.EmployeeSpecialty
                                                            .ToDictionary(d => d.OrganizationSpecialtyType.SpecialtyTypeID, d => d.OrganizationSpecialtyType.Name)
                                    }
                        );

In the EmployeeDTO class the property Specialty is type public Dictionary<int, string> .

If I execute this query, everything works normally:

var spec = _context.Employee.Where(p => p.EmployeeID == -9070).FirstOrDefault()
    .EmployeeSpecialty.ToDictionary(d =>
         d.OrganizationSpecialtyType.SpecialtyTypeID,
         d => d.OrganizationSpecialtyType.Name);

How I can solve my first query to obtain EmployeeDTO with specialties?

Thanks.

Answer 1

You can select to anonymous type first, then set the dictionary later.

var q = _context.Employee.Where(p => employeeEMIIDs.Contains(p.EmployeeID))
    .Select(p => new
    {
        Employee = new EmployeeDTO
        {
             EmployeeID = p.EmployeeID,
             GenderTypeID = p.GenderTypeID,
             FirstName = p.FirstName,
             LastName = p.LastName,
             Name = p.Name,
             MiddleName = p.MiddleName,
             DOB = p.DOB,
             Suffix = p.Suffix,
             Title = p.Title
         },
         Specialty = p.EmployeeSpecialty
             .Select(d => new 
             {
                 d.OrganizationSpecialtyType.SpecialtyTypeID,
                 d.OrganizationSpecialtyType.Name
             })
    })                    
    .AsEnumerable()
    .Select(a => 
    {
        a.Employee.Specialty = a.Specialty
            .ToDictionary(d => d.SpecialtyTypeID, d => d.Name);
        return a.Employee;
    });