How to query generic list using LINQ?

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foreach (T setName in setNames)
{
 List<T> list = objectList.Where(x => x.QualificationID == setName).ToList();
 redisClient.SetAdd<string>("Qualification:" + setName, list.Select(x => x.ProductID).ToString());
}

In Line 3, T does not contain a definition for 'QualificationID' and no extension method 'QualificationID' accepting a first argument of Type T could be found.
Similarly in Line 4,
T does not contain a definition for 'ProductID' and no extension method 'ProductID' accepting a first argument of Type T could be found

How can we query the list of generic type?

What I have tried:

foreach (T setName in setNames)
{
 List<T> list = objectList.Where(x => x.QualificationID == setName).ToList();
 redisClient.SetAdd<string>("Qualification:" + setName, list.Select(x => x.ProductID).ToString());
}

Posted 30-Apr-17 21:12pm

Member 1097736

Updated 30-Apr-17 21:59pm

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OriginalGriff · Answer 1 · 2017-04-30T21:59:00

When you use generic methods, it "fills in the blanks" from the type of the collection - so the properties and methods you can use on each object depends on the type of the collection.
So a collection of Point object can use Point propertuies:

C#

List<Point> points = GetPoints();
List<Point> leftColumn = points.Where(p => p.X <= 10).ToList();

But a collection of strings would let you use string properties:

C#

List<string> strings = GetStrings();
List<string> shortStrings = strings.Where(s => s.Length <= 10).ToList();

Whatever your collection is declared as determines what properties and methods you can use inside your class, not what items in the collection may be. So if you use a base class:

C#

List<object> strings = GetStrings();
List<string> shortStrings = strings.Where(s => s.Length <= 10).ToList();

You will get an error because Length is not a property of the object class, even if all the objects in the collection are strings, and have a Length - the system doesn't "know" that all the objects in the class will always be strings:

C#

List<object> strings = new List<object>();
strings.Add("Hello!");
strings.Add(666);
strigns.Add(new Point(12, 42));
List<string> shortStrings = strings.Where(s => s.Length <= 10).ToList();

So look to what setNames is declared as - that controls what properties you can use.