如何重载Linq的Where子句以接受SqlBoolean？

Question

Linq's Where clause works with booleans. How do you get it to work with sqlBooleans. Here is sample code to illustrate the problem

// Trivia example to draw attention to the problem 
var nodeCollection = new List<SqlBoolean>();
nodeCollection.Add(SqlBoolean.Parse("0"));
nodeCollection.Add(SqlBoolean.Parse("1"));
nodeCollection.Add(SqlBoolean.Parse("1"));

var nodeA = SqlBoolean.Parse("1");
var trueOne = nodeCollection.Where(n => n == nodeA); // Error message, cannot convert SqlBoolean to bool

You get an error since the result of the predicate is SqlBoolean rather than bool. How do you extend the Where clause to make this work. Using casting, SqlBoolean's Value, IsTrue and IsFalse are not desirable.

Answer 1

You have to convert the SqlBoolean to a bool . You can cast it explicitly :

var trueOne = nodeCollection.Where(n => (bool)(n == nodeA));  

or compare the Value property:

var trueOne = nodeCollection.Where(n => n.Value == nodeA.Value); 

The problem is that SqlBoolean == SqlBoolean returns SqlBoolean not bool since the equality operator is overridden .

Answer 2

You could create an extension method to wrap the Where :

public static IEnumerable<T> WhereSqlBoolean<T>(
    this IEnumerable<T> source, Func<T,SqlBoolean> condition) {
    return source.Where(t => (bool)condition(t));
}

Still not the cleanest, but works:

var trueOne = nodeCollection.WhereSqlBoolean(n => n == nodeA);