c# - Linq2sql 泛型按列和值选择

Question

我正在使用泛型使用 linq2sql 从数据库中执行一些基本的插入/更新/选择。

我有以下内容，我试图将其转换为接受列名和对象值以根据其进行选择，但我无法让它工作。

public static T SelectByID<T>(string id) where T : class
{
    try
    {
        using (DataContext db = new DataContext(CHCGlobal.ConnectionString))
        {
            //get Table of type T
            var table = db.GetTable<T>();

            //get object mappings
            MetaModel modelMap = table.Context.Mapping;

            //get the data members for this type
            ReadOnlyCollection<MetaDataMember> dataMembers = modelMap.GetMetaType(typeof(T)).DataMembers;

            //find primary key
            string pk = (dataMembers.Single<MetaDataMember>(m => m.IsPrimaryKey)).Name;

            //return a single object with the id matching the pk field
            return table.SingleOrDefault<T>(delegate (T t)
            {
                string memberId = t.GetType().GetProperty(pk).GetValue(t, null).ToString();
                return memberId.ToString() == id.ToString();
            });
        }
    }
    catch (Exception)
    {
        throw;
    }
}

这是我试图创建的函数，但我卡在了 select 语句上。

public static List<T> SelectByKeyValue<T>(string id, object value) where T : class
{
    try
    {
        using (DataContext db = new DataContext(CHCGlobal.ConnectionString))
        {
            //get Table of type T
            var table = db.GetTable<T>();

            //get object mappings
            MetaModel modelMap = table.Context.Mapping;

            //get the data members for this type
            ReadOnlyCollection<MetaDataMember> dataMembers = modelMap.GetMetaType(typeof(T)).DataMembers;

            //find key
            string pk = (dataMembers.Single<MetaDataMember>(m => m.Name.Equals(id))).Name;

            //NOT WORKING
            return table.Select<T, T>(delegate (T t)
            {
                var memberID = t.GetType().GetProperty(pk).GetValue(t, null);
                return memberID.Equals(value);
            }).ToList<T>();
        }
    }
    catch (Exception)
    {
        throw;
    }
}

Answer 1

You have to use Where, not Select.

Select transforms N items into N new items, it doesn't filter.
Where does that.

return table.Where(t => t.GetType().GetProperty(pk).GetValue(t, null)
                         .Equals(value))
            .ToList();