c# 拼接lambda表达式 （转载）

项目中用到，找不到出处了

1. 添加类：

public static class PredicateExtensions
    {
        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>> expression1, Expression<Func<T, bool>> expression2)
        {
            var invokedExpression = Expression.Invoke(expression2, expression1.Parameters.Cast<Expression>());
            return Expression.Lambda<Func<T, bool>>(Expression.Or(expression1.Body, invokedExpression), expression1.Parameters);
        }

        public static Expression<Func<T, bool>> And<T>(this Expression<Func<T, bool>> expression1, Expression<Func<T, bool>> expression2)
        {
            var invokedExpression = Expression.Invoke(expression2, expression1.Parameters.Cast<Expression>());
            return Expression.Lambda<Func<T, bool>>(Expression.And(expression1.Body, invokedExpression), expression1.Parameters);
        }
    }

 

2. 用法：

     Expression<Func<XXX, bool>> expression = t => true;
     expression = expression.And(t => t.AAA == 1);
     expression = expression.And(t => t.BBB > 1);
     var ds = products.AsQueryable().Where(expression).ToList();