CODEWITHSUNDEEP
linqexpression-trees
Nick Kahn
Nick Kahn

Reputation: 20078

Building Linq Query Dynamically

I'm writing LINQ query that implements a keyword-style search. In other words, a query that returns rows whose Title,Description,Id contains

As follows

    public static IQueryable<EmployeeObject> QueryableSQL()
    {
        IQueryable<EmployeeObject> queryable = EmployeeRepository.GetAllEmployee(); 
    }

    public static IList<EmployeeObject> QLike(string txt)
    {
       IList<employeeObject> _emps = QueryableSQL().Where(x => x.Title == txt).ToList();
       return _emps;
    }

So far, so good. But this only handles the case where you want to match in my case Title.

Suppose instead, I wanted to search based on the 'DescriptionorIdshould i have to create a new method for Description? or is there a way i can create aTree expression`

Upvotes: 3

Views: 106

Answers (3)

gleng
gleng

Reputation: 6304

public static IQueryable<EmployeeObject> QueryableSQL()
{
    IQueryable<MediaObject> queryable = EmployeeRepository.GetAllEmployee(); 
}

public static IList<EmployeeObject> QLike(Expression<Func<EmployeeObject, bool>> func)
{
   return QueryableSQL().Where(func).ToList();
}

You can then call this like:

QLike(t => t.Title == "MyText");

Upvotes: 3

dmck
dmck

Reputation: 7861

It sounds like you want the property you are comparing against to by dynamic, you could use reflection to do this:

public static IList<EmployeeObject> QLike(string propName, string txt)
{
   PropertyInfo filterProp = typeof(EmployeeObject).GetProperty(propName);
   IList<employeeObject> _emps = QueryableSQL().Where(x => filterProp.GetValue(x, null).ToString() == txt).ToList();
   return _emps;
}

However the downside to this approach is that you are going to end up loading all of the objects from the database and then filtering them in your code.

If you follow the approach @gleng shows then the Ling to SQL provide will be able to do the filtering in the generated SQL statement. You do need to code the predicates upfront in that case and call the appropriate one based on what property you want to call.

Upvotes: 2

Ani
Ani

Reputation: 10896

Have you looked at Dynamic Linq? That is, of course if this text may be user provided instead of compiled.

Upvotes: 2

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