Question

I am using a Data Entity from the db, and a Domain Service.

I am using .net’s generated code for the simple queries, like this

public IQueryable<employee> GetEmployeesByLocale(int localeID)
{
    return ObjectContext.employees.Where(e => e.Locale_ID == localeID);
}

Now, I need to change the .Where section accordingly, so:

if (localeID > 0)
{
    ['Where' should be like .Where(e => e.Locale_ID == localeID)];
}
if (projectID > 0)
{
    [IF localeID == 0, 'Where' should be like .Where(e => e.Project_ID == projectID)
    Else if localeID > 0, Where should use both, sort of .Where(e => e.Locale_ID == localeID && e.Project_ID == projectID)];
}

and so on with other variables.

There are many possible combinations , which is why I was trying to use the overload for .Where(string, parameter[])

string q = string.Empty;
if (localeID > 0)
{
    q = "Locale_ID = " + localeID.ToString();
}

if (projectID > 0)
{
    q = q == string.Empty ? "Project_ID = " + projectID.ToString() : q + " and " + "Project_ID = " + projectID.ToString();
}
... (for other variables and fields)
...
System.Data.Objects.ObjectParameter[] param = new System.Data.Objects.ObjectParameter[1];
param[0] = new System.Data.Objects.ObjectParameter("param", 1);
return ObjectContext.employees.Where(q, param);

However, this only gives an error, because then all the fieldnames are supposedly out-of-scope/non-existing. Even if use employees.[field_name] in the string, they “don’t exist”

Does anyone know of a way to use conditionals inside the .Where part of the query? Or how to create some var or object containing my query so I can just parse it?

Answer 1

You can use

IQueryable<Employee> emp =  ObjectContext.employees;
if (localeID > 0)  
    emp=emp.Where(e => e.Locale_ID == localeID).AsQueryable();  

if (projectID > 0)  
    emp=emp.Where(e => e.Project_ID == projectID).AsQueryable();  

This will concatenate the where clauses