C# Tuples

Tuples in C# provide a way for "one" object to have multiple types and values.  I use this a lot when I'm returning results from one method to another so I can check whether the call was successful (with a bool) and also return a value (like an error message) to the caller.

You use Tuples by specifying - through the use of generic type parameters - what the data types will be of each "item" in the tuple.  Each tuple can have seven items, and an eighth item that is another tuple.

In our home-grown ORM solution I've implemented tuples as the return type of the methods that map data from the database to the objects:

   1:  Tuple<TParent, TChild1, TChild2, TChild3, TChild4, TChild5, TChild6> Get

   2:              <TParent, TChild1, TChild2, TChild3, TChild4, TChild5, TChild6>(string sprocName,

   3:                                                                              List<SqlParameter> parameters = null,

   4:                                                                              string schema = "dbo",

   5:                                                                              CommandType commandType =

   6:                                                                                  CommandType.StoredProcedure)

   7:              where TParent : class

   8:              where TChild1 : class

   9:              where TChild2 : class

  10:              where TChild3 : class

  11:              where TChild4 : class

  12:              where TChild5 : class

  13:              where TChild6 : class;

This method will return a single object with a total of 7 items where there is one parent object that has six properties that are each a complex object.  When I invoke this method, I do so like this:

   1:  var data = Get<Person, List<Pet>, List<Car>, Person, List<Person>, House, Employer>("Person_GetDetails", new List<SqlParameter> {new SqlParameter("@ID", 12345)});

   2:   

   3:  var person = data.Item1;

   4:  person.Pets = data.Item2;

   5:  person.Cars = data.Item3;

   6:  person.Spouse = data.Item4;

   7:  person.House = data.Item5;

   8:  person.Employer = data.Item6;

This way I can pass back a single Person object from my repository method.  There are, of course, other uses, but this is a quick example of how to use tuples.