static LambdaExpression InternalAndOrExpression(bool condition, LambdaExpression exp1, LambdaExpression exp2, bool isAndAlso)
{
if (condition == false)
{
return(exp1);
}
if (exp1 == null)
{
return(exp2);
}
if (exp2 == null)
{
return(exp1);
}
var newParameters = exp1.Parameters.Select((a, b) => Expression.Parameter(a.Type, $"new{b}")).ToArray();
var left = new NewExpressionVisitor(newParameters, exp2.Parameters.ToArray()).Replace(exp1.Body);
var right = new NewExpressionVisitor(newParameters, exp2.Parameters.ToArray()).Replace(exp2.Body);
var body = isAndAlso ? Expression.AndAlso(left, right) : Expression.OrElse(left, right);
return(Expression.Lambda(exp1.Type, body, newParameters));
}
/// <summary>
/// 使用 or 拼接两个 lambda 表达式
/// </summary>
/// <typeparam name="T"></typeparam>
/// <param name="exp1"></param>
/// <param name="condition">true 时生效</param>
/// <param name="exp2"></param>
/// <returns></returns>
public static Expression <Func <T, bool> > Or <T>(this Expression <Func <T, bool> > exp1, bool condition, Expression <Func <T, bool> > exp2)
{
if (condition == false)
{
return(exp1);
}
if (exp1 == null)
{
return(exp2);
}
if (exp2 == null)
{
return(exp1);
}
ParameterExpression newParameter = Expression.Parameter(typeof(T), "c");
NewExpressionVisitor visitor = new NewExpressionVisitor(newParameter, exp2.Parameters.FirstOrDefault());
var left = visitor.Replace(exp1.Body);
var right = visitor.Replace(exp2.Body);
var body = Expression.OrElse(left, right);
return(Expression.Lambda <Func <T, bool> >(body, newParameter));
}
