/// <summary>
/// expr1 or expr2
/// </summary>
/// <typeparam name="T"></typeparam>
/// <param name="expr1"></param>
/// <param name="expr2"></param>
/// <returns></returns>
public static Expression <Func <T, bool> > Or <T>(this Expression <Func <T, bool> > expr1, Expression <Func <T, bool> > expr2)
{
if (expr1 == null)
{
return(expr2);
}
else if (expr2 == null)
{
return(expr1);
}
ParameterExpression newParameter = Expression.Parameter(typeof(T), "c");
NewExpressionVisitor visitor = new NewExpressionVisitor(newParameter);
var left = visitor.Replace(expr1.Body);
var right = visitor.Replace(expr2.Body);
var body = Expression.Or(left, right);
return(Expression.Lambda <Func <T, bool> >(body, newParameter));
}
/// <summary>
/// expr1 AND expr2
/// </summary>
/// <typeparam name="T"></typeparam>
/// <param name="expr1"></param>
/// <param name="expr2"></param>
/// <returns></returns>
public static Expression <Func <T, bool> > And <T>(this Expression <Func <T, bool> > expr1, Expression <Func <T, bool> > expr2)
{
if (expr1 == null)
{
return(expr2);
}
else if (expr2 == null)
{
return(expr1);
}
//This will not work which has error when compile new expression. the artuments in expr1.Parameters is not the one in expr2.Body.
//return Expression.Lambda<Func<T, bool>>(Expression.AndAlso(expr1.Body, expr2.Body), expr1.Parameters);
ParameterExpression newParameter = Expression.Parameter(typeof(T), "c");
NewExpressionVisitor visitor = new NewExpressionVisitor(newParameter);
//Put bodies of expr1 and expr2 in to a new expression
var left = visitor.Replace(expr1.Body);
var right = visitor.Replace(expr2.Body);
var body = Expression.And(left, right);
return(Expression.Lambda <Func <T, bool> >(body, newParameter));
}