将两个方法合并为一个泛型方法

本文关键字：一个 泛型方法 两个 方法 合并 | 更新日期: 2023-09-27 18:22:17

我的DAL中有两个方法，它们完全相同，并基于作为参数支持的主键返回数据库行。DB上下文是linqtoSQL。一个传入字符串参数，另一个传入int参数。我认为必须使用泛型来创建一个接受string或int但不确定如何接受的方法。

    /// <summary>
    /// Select table row by integer Primary Key Value
    /// </summary>
    /// <typeparam name="T"></typeparam>
    /// <param name="id">The PK value to search for</param>
    /// <returns>Single matching PK to id</returns>
    public T SelectRowByPk<T>(int id) where T : class
    {
        using (var dc = new DBDataContext())
        {
            // Get the table by the type passed in
            var table = dc.GetTable<T>();
            // Get the metamodel mappings (database to domain objects)
            MetaModel modelMap = table.Context.Mapping;
            // Get the data members for this type
            ReadOnlyCollection<MetaDataMember> dataMembers =  
            modelMap.GetMetaType(typeof (T)).DataMembers;
            // Find the primary key field name by checking for IsPrimaryKey
            string pk = (dataMembers.Single(m => m.IsPrimaryKey)).Name;
            // Return a single object where the id argument matches the primary key 
            field value
            return table.SingleOrDefault(delegate(T t)
                                            {
                                                int memberId =
  Convert.ToInt16(t.GetType().GetProperty(pk).GetValue(t, null));
                                                return memberId == id;
                                            });
        }
    }
    /// <summary>
    /// Select table row by Varchar Primary Key Value
    /// </summary>
    /// <typeparam name="T"></typeparam>
    /// <param name="id">The PK value to search for</param>
    /// <returns>Single matching PK to id</returns>
    public T SelectRowByVarcharPk<T>(string id) where T : class
    {
        using (var dc = new DBDataContext())
        {
            // Get the table by the type passed in
            var table = dc.GetTable<T>();
            // Get the metamodel mappings (database to domain objects)
            MetaModel modelMap = table.Context.Mapping;
            // Get the data members for this type
            ReadOnlyCollection<MetaDataMember> dataMembers = 
  modelMap.GetMetaType(typeof(T)).DataMembers;
            // Find the primary key field name by checking for IsPrimaryKey
            string pk = (dataMembers.Single(m => m.IsPrimaryKey)).Name;
            // Return a single object where the id argument matches the primary key 
 field value
            return table.SingleOrDefault(delegate(T t)
            {
                string memberId =
                   t.GetType().GetProperty(pk).GetValue(t, null).ToString();
                return memberId == id;
            });
        }
    }

将两个方法合并为一个泛型方法

您不能直接使用泛型将两个方法组合为一个方法，但是您可以将一些重构与泛型结合使用，以获得干净的设计：

制作一个私有方法，使用两个通用参数来完成繁重的工作，一个用于实体类型，另一个用于主键类型：

 private T SelectRowById<T, TId>(TId id) where T : class
    {
        using (var dc = new DBDataContext())
        {
            // Get the table by the type passed in
            var table = dc.GetTable<T>();
            // Get the metamodel mappings (database to domain objects)
            MetaModel modelMap = table.Context.Mapping;
            // Get the data members for this type
            ReadOnlyCollection<MetaDataMember> dataMembers = 
  modelMap.GetMetaType(typeof(T)).DataMembers;
            // Find the primary key field name by checking for IsPrimaryKey
            string pk = (dataMembers.Single(m => m.IsPrimaryKey)).Name;
            // Return a single object where the id argument matches the primary key 
 field value
            return table.SingleOrDefault(delegate(T t)
            {
                var memberId =
                   (TId)t.GetType().GetProperty(pk).GetValue(t, null);
                return memberId == id;
            });
        }
    }

之后，您可以为使用此私有方法的特定id类型声明两个公共方法：

public T SelectRowById<T>(string id) where T : class
{
   return SelectRowById<T, string>(id);
}
public T SelectRowById<T>(int id) where T : class
{
   return SelectRowById<T, int>(id);
}

通过这种方式，您将拥有一个干净的公共界面，代码重复最少。

public T SelectRowByPk<T>(T id)
{
    //you'll need to do some run-time type checking of 'id' here since string and int
    //can't be constrained by a type parameter constraint in the same method
}

指定类型参数的要点之一是可以具有动态参数类型。在本例中，"id"将变为您指定的任何类型。

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