C Pass Lambda Expression as Method Parameter

Question

I have a lambda expression that I d like to be able to pass around and reuse   Here s the code   public List lt IJob gt  getJobs    i want to pass the lambda expr in here         using  SqlConnection connection   new SqlConnection getConnectionString           connection Open        return connection Query lt FullTimeJob  Student  FullTimeJob gt  sql          job  student    gt                     job Student   student          job StudentId   student Id          return job                     splitOn   user id           param  parameters  ToList lt IJob gt                 The key here  is I want to be able to pass the lambda expression that I m using here into the method that s calling this code  so I can reuse it   The lambda expression is the second argument inside my  Query method  I m assuming I d want to use an Action or Func  but I m not quite sure what the syntax is for this or how it quite works   Can someone please give me an example

User · Answer

You should use a delegate type and specify that as your command parameter. You could use one of the built in delegate types - Action and Func.

In your case, it looks like your delegate takes two parameters, and returns a result, so you could use Func:

List<IJob> GetJobs(Func<FullTimeJob, Student, FullTimeJob> projection)

You could then call your GetJobs method passing in a delegate instance. This could be a method which matches that signature, an anonymous delegate, or a lambda expression.

P.S. You should use PascalCase for method names - GetJobs, not getJobs.

User · Answer

If I understand you need following code   passing expression lambda by parameter  The Method  public static void Method Expression lt Func lt int  bool gt  gt  predicate         int   number  1 2 3 4 5 6 7 8 9 10       var newList   from x in number                    Where predicate Compile      here compile your clausuly                   select x                  newList ToList     return a new list         Calling method  Method v   gt  v Equals 1      You can do the same in their class  see this is example   public string Name  get set    public static List lt Class gt  GetList Expression lt Func lt Class  bool gt  gt  predicate                List lt Class gt  c   new List lt Class gt             c Add new Class  name1             c Add new Class  name2              var f   from g in c                  Where  predicate Compile                    select g          f ToList            return f          Calling method  Class GetList c  gt c Name   yourname      I hope this is useful

User · Answer

Lambda expressions have a type of Action lt parameters gt   in case they don t return a value  or Func lt parameters return gt   in case they have a return value   In your case you have two input parameters  and you need to return a value  so you should use   Func lt FullTimeJob  Student  FullTimeJob gt

User · Answer

Use a Func lt T1  T2  TResult gt  delegate as the parameter type and pass it in to your Query   public List lt IJob gt  getJobs Func lt FullTimeJob  Student  FullTimeJob gt  lambda      using  SqlConnection connection   new SqlConnection getConnectionString           connection Open        return connection Query lt FullTimeJob  Student  FullTimeJob gt  sql           lambda          splitOn   user id           param  parameters  ToList lt IJob gt                  You would call it   getJobs  job  student    gt                     job Student   student          job StudentId   student Id          return job                Or assign the lambda to a variable and pass it in

[c#] C# Pass Lambda Expression as Method Parameter

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