I've a list of expressions:
List<Expression<Func<Domain.FollowUpActivity, bool>>> fuaExpressions = null;
I need to join all of them on a single OR expression: I've tried this:
Expression body = Expression.Constant(false);
foreach (var orExpression in orExpressions)
foreach (Expression orExp in orExpression.Expressions)
body = Expression.Or(body, orExp);
It throws me an InvalidOperationException
due to boolean operator is not defined between Expression<Boolean>
and Expression<Func<T, bool>>
Some help please?
From a great book by Albahari brothers:
public static class PredicateBuilder
{
public static Expression<Func<T, bool>> True<T> () { return f => true; }
public static Expression<Func<T, bool>> False<T> () { return f => false; }
public static Expression<Func<T, bool>> Or<T> (this Expression<Func<T, bool>> expr1,
Expression<Func<T, bool>> expr2)
{
var invokedExpr = Expression.Invoke (expr2, expr1.Parameters.Cast<Expression> ());
return Expression.Lambda<Func<T, bool>>
(Expression.OrElse (expr1.Body, invokedExpr), expr1.Parameters);
}
public static Expression<Func<T, bool>> And<T> (this Expression<Func<T, bool>> expr1,
Expression<Func<T, bool>> expr2)
{
var invokedExpr = Expression.Invoke (expr2, expr1.Parameters.Cast<Expression> ());
return Expression.Lambda<Func<T, bool>>
(Expression.AndAlso (expr1.Body, invokedExpr), expr1.Parameters);
}
}
Use it like this:
List<Expression<Func<Domain.FollowUpActivity, bool>>> fuaExpressions = null;
Expression<Func<Domain.FollowUpActivity, bool>> result = PredicateBuilder.False<Domain.FollowUpActivity>();
foreach (var exp in fuaExpressions)
{
result = PredicateBuilder.Or(result, exp);
}
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