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();