linq to sql 动态构建查询表达式树

通过Expression类进行动态构造lamda表达式。

实现了以下几种类型，好了代码说话：

public Expression<Func<T, bool>> GetAndLambdaExpression<T>(string[] keys,object[] values,string[] methons)
{

Expression expression_return = Expression.Constant(true);
Type TType = typeof(T);
ParameterExpression expression_param = Expression.Parameter(TType, "p");
Expression temp;
for (int i = 0; i < keys.Length; i++)
{
    switch (methons[i])
    {
        case "=":
            temp = Expression.Equal(Expression.Call(Expression.Property(expression_param, TType.GetProperty(keys[i])),
                TType.GetMethod("ToString")),
             Expression.Constant(values[i]));
            expression_return = Expression.And(expression_return, temp);
            break;
        case "%":
            temp = Expression.Call(Expression.Property(expression_param, TType.GetProperty(keys[i])),
                typeof(string).GetMethod("Contains"),
                Expression.Constant(values[i], typeof(string)));
            expression_return = Expression.And(expression_return, temp);
            break;
        case ">":
            //temp = Expression.Call(Expression.Property(expression_param, TType.GetProperty(keys[i])),
            //    TType.GetProperty(keys[i]).GetType().GetMethod("GreaterThan"), Expression.Constant(values[i]));
            temp = Expression.GreaterThan(Expression.Property(expression_param, TType.GetProperty(keys[i])), Expression.Constant(Convert.ToInt32(values[i])));
            expression_return = Expression.And(expression_return, temp);
            break;
        case "<":
            //temp = Expression.Call(Expression.Property(expression_param, TType.GetProperty(keys[i])),
            //   Expression.GetType().GetMethod("LessThan"), Expression.Constant(values[i]));
            temp=Expression.LessThan(Expression.Property(expression_param, TType.GetProperty(keys[i])), Expression.Constant(Convert.ToInt32(values[i])));
            expression_return = Expression.And(expression_return, temp);
            break;
        case ">=":
            //temp = Expression.Call(Expression.Property(expression_param, TType.GetProperty(keys[i])),
            //    TType.GetProperty(keys[i]).GetType().GetMethod("GreaterThanOrEqual"), Expression.Constant(values[i]));
            temp = Expression.GreaterThanOrEqual(Expression.Property(expression_param, TType.GetProperty(keys[i])), Expression.Constant(Convert.ToInt32(values[i])));
            expression_return = Expression.And(expression_return, temp);
            break;
        case "<=":
            //temp = Expression.Call(Expression.Property(expression_param, TType.GetProperty(keys[i])),
            //    TType.GetProperty(keys[i]).GetType().GetMethod("LessThanOrEqual"), Expression.Constant(values[i]));
            temp = Expression.LessThanOrEqual(Expression.Property(expression_param, TType.GetProperty(keys[i])), Expression.Constant(Convert.ToInt32(values[i])));
            expression_return = Expression.And(expression_return, temp);
            break;
        case "in":
            string[] strarr = values[i].ToString().Split(',');
            Expression or_return = Expression.Constant(false);
            for (int k = 0; k < strarr.Length; k++)
            {
                temp = Expression.Equal(Expression.Call(Expression.Property(expression_param, TType.GetProperty(keys[i])),
                    TType.GetMethod("ToString")),
                 Expression.Constant(strarr[k]));
                or_return = Expression.Or(or_return, temp);
            }
 
            expression_return = Expression.And(expression_return, or_return);
            break;
    }
}
 
return (Expression<Func<T, bool>>)Expression.Lambda<Func<T, bool>>(expression_return, new ParameterExpression[] { expression_param });

}

　　　　　　　IList<People> peopleList = new List<People>();
            for (int i = 1; i <= 6; i++)
            {
                People people = new People() { Name = "Dai_" + i.ToString(), Age = 16, Birthday = DateTime.Now, IsBuyCar = true, Sex = "F" };
                peopleList.Add(people);
            }
            Expression<Func<People, bool>> func_a = GetAndLambdaExpression<People>(new string[] { "Name", "Age" }, new string[] { "Dai_2", "16" }, new string[] { "=", "<" });
            var people_data = peopleList.AsEnumerable().Where(func_a.Compile()).ToList();