使用Enterprise Library的ExecuteSprocAccessor方法和泛型 [英] Using Enterprise Library's ExecuteSprocAccessor method with generics

问题描述

我尝试使用.NET Enterprise Library的泛型的ExecuteSprocAccessor方法来使用一个类来处理数据库上的所有CRUD。在我的数据层中，我正在尝试如下所示：

I am trying to use one class to handle all of my CRUD on the database by using the ExecuteSprocAccessor method of the .NET Enterprise Library with generics. In my data layer, I was trying something like this:

public static class CRUDDatabase
{
    private static Database db = DatabaseFactory.CreateDatabase("ITS");

    public static T SelectSingle<T>(string sprocName, int id)
    {
        return db.ExecuteSprocAccessor<T>(sprocName, id).First();
    }
}

但是，我在返回行中遇到了构建错误在SelectSingle（）方法中声明：

However, I get a build error on the return line in the SelectSingle() method that states:

'T'必须是一个具有公共无参数$ b的非抽象类型$ b构造函数以便将其用作通用
类型或方法中的参数'TResult'
'Microsoft.Practices.EnterpriseLibrary.Data.DatabaseExtensions.ExecuteSprocAccessor（Microsoft.Practices.EnterpriseLibrary.Data.Database，
string，params object []）'

SelectSingle（）从数据库传入存储过程名称和所需对象的记录标识。最终我会有SelectAll（），Update（），Delete（）等等。这些方法中的参数会有所不同，但您可以了解我正在努力完成的任务。

The idea behind the SelectSingle() method is that you pass in the stored procedure name and the record id of the object you want from the database. Eventually I would have SelectAll(), Update(), Delete(), etc. The parameters in those methods would be different, but you get the idea of what I'm trying to accomplish.

在阅读完这个错误之后，我开始认为这可能是不可能的，但是有谁知道这是否可行？此外，数据库中的字段与我的类中的字段匹配1：1，所以这就是为什么我没有指定任何映射器。

After reading that error, I am beginning to think this may be impossible, but does anyone know if this can work? Also, my fields in the database match 1:1 with the fields in my classes, so that is why I am not specifying any mappers.

谢谢

推荐答案

编译器告诉你什么是错误的：它期望一个类型的零参数公共构造函数。所有你交给它的是T，它不能作任何保证，所以它不会编译。

The compiler is telling you what's wrong: it's expecting a type that's got a zero-argument public constructor on it. All you've handed it is T, which it can't make any guarantees on, so it won't compile.

你需要添加一个通用约束来限制类型T可以。幸运的是，这非常简单：

You need to add a generic constraint to limit the types T can be. Luckily, that's trivially easy:

public static T SelectSingle<T>(string sprocName, int id)    
    where T : new()  // <---- here's the constraint
{
    return db.ExecuteSprocAccessor<T>(sprocName, id).First();    
}

它告诉编译器任何传入的类型必须有一个零参数构造函数。

That tells the compiler "Any type passed here must have a zero-argument constructor.

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