Question

In another posting: Does Linq-To-Sql support composable queries there was discussion on how to compose/concat where clauses dynamically. This appears to be done with an ‘AND’ (i.e. the first where clause and the second where clause are joined by an AND). What I am wondering is if there is a way to compose Linq queries with an OR.

Example:

var people = from p in Person              where p.age < 18              select p  var otherPeople = from p in people                   where p.firstName equals 'Daniel'                   select p 

This gives people with a first name of ‘Daniel’ and that are under 18. I’m looking for the syntax to join these to find people who have a first name of ‘Daniel’ or are under 18.

Note: I am using ADO.net Data Services so I do not have .Contains() available to me.

EDIT: The Union Suggestion (by Garry Shutler) is exactly what I am looking for functionality-wise. I did run into two possible issues with it:

1. It looks like it would make multiple database hits if I was to do a third condition (union seems to take an IEnumerable as its parameter) – I was hoping to build up multiple AND and OR statements in code and then execute one request.
2. Union is not supported by ADO.Net Data Services (very disappointing)

Answer 1

Is what you want as simple as:

var people = from p in Person              where p.age < 18 || p.firstName == 'Daniel'              select p; 

or have you just given a simple example?

In which case you can use:

var under18 = from p in Person               where p.age < 18               select p;  var daniels = from p in Person               where p.firstName == 'Daniel'               select p;  var combined = under18.Union(daniels); 

LinqToSql may be intelligent enough to convert that to an OR but I’m not so sure.