C# 如何使用存储库和Web API选择不同的数据源实例？

我使用的是一个存储库，它在将子集返回给调用方之前填充要使用和查询的数据。下面是一个例子

控制器的代码如下所示：

public class DuckbillItemsController : ApiController
{
    static readonly IDuckbillItemRepository DuckbillItemsRepository = new DuckbillItemRepository();

    public IEnumerable<DuckbillItem> GetBatchOfDuckbillItemsByStartingID(string ID, int CountToFetch)
    {
        return DuckbillItemsRepository.Get(ID, CountToFetch);
    }
}

public class DuckbillItemsController : ApiController
{
    static readonly IDuckbillItemRepository DuckbillItemsRepository1 = new DuckbillItemRepository(1);
    static readonly IDuckbillItemRepository DuckbillItemsRepository2 = new DuckbillItemRepository(2);
    static readonly IDuckbillItemRepository DuckbillItemsRepository3 = new DuckbillItemRepository(3);
. . .

    public IEnumerable<DuckbillItem> GetBatchOfDuckbillItemsByStartingID(int DBSpecifier, string ID, int CountToFetch)
    {
        if (DBSpecifier == 1)
        {
                return DuckbillItemsRepository1.Get(ID, CountToFetch);
        }
        else if (DBSpecifier == 2)
        {
                return DuckbillItemsRepository2.Get(ID, CountToFetch);
        }
        else if (DBSpecifier == 3)
        {
                return DuckbillItemsRepository3.Get(ID, CountToFetch);
        }
. . .
    }
}

public DuckbillItemRepository(int DBSpecifier)
{
    string id = string.Empty;

    try
    {
        if (DBSpecifier == 1)
       {
            using (var conn = new OleDbConnection(
                @"Provider=Microsoft.Jet.OLEDB.4.0;User ID=NRBQNRotPS;Password=NRBQNRotPS;Data Source=C:\PlatypusWin\DATA\PlatypusDAT01.MDB;Jet OLEDB:System database=C:\PlatypusWin\Data\NRBQ.mdw"))
       }
       else if (DBSpecifier == 2)
       {
            using (var conn = new OleDbConnection(
                @"Provider=Microsoft.Jet.OLEDB.4.0;User ID=NRBQNRotPS;Password=NRBQNRotPS;Data Source=C:\PlatypusWin\DATA\PlatypusDAT02.MDB;Jet OLEDB:System database=C:\PlatypusWin\Data\NRBQ.mdw"))
       }
       else if (DBSpecifier == 3)
       {
            using (var conn = new OleDbConnection(
                @"Provider=Microsoft.Jet.OLEDB.4.0;User ID=NRBQNRotPS;Password=NRBQNRotPS;Data Source=C:\PlatypusWin\DATA\PlatypusDAT03.MDB;Jet OLEDB:System database=C:\PlatypusWin\Data\NRBQ.mdw"))
       }
       . . .

return Repositories[DBSpecifier].Get(ID, CountToFetch);

using (var conn = new OleDbConnection(Repositories[DBSpecifier]))

……为此：

string uri = String.Format("http://platypi:28642/api/Duckbills/{0}/{1}/{2}", DBSpecifier, lastIdFetched, RECORDS_TO_FETCH);

对吧?？但如果是这样，我如何提醒我的控制器根据所需的DB实例调用重载构造函数？我是否需要将控制器代码更改为以下内容：

public class DuckbillItemsController : ApiController
{
    static readonly IDuckbillItemRepository DuckbillItemsRepository = new DuckbillItemRepository();

    public IEnumerable<DuckbillItem> GetBatchOfDuckbillItemsByStartingID(string ID, int CountToFetch)
    {
        return DuckbillItemsRepository.Get(ID, CountToFetch);
    }
}

public class DuckbillItemsController : ApiController
{
    static readonly IDuckbillItemRepository DuckbillItemsRepository1 = new DuckbillItemRepository(1);
    static readonly IDuckbillItemRepository DuckbillItemsRepository2 = new DuckbillItemRepository(2);
    static readonly IDuckbillItemRepository DuckbillItemsRepository3 = new DuckbillItemRepository(3);
. . .

    public IEnumerable<DuckbillItem> GetBatchOfDuckbillItemsByStartingID(int DBSpecifier, string ID, int CountToFetch)
    {
        if (DBSpecifier == 1)
        {
                return DuckbillItemsRepository1.Get(ID, CountToFetch);
        }
        else if (DBSpecifier == 2)
        {
                return DuckbillItemsRepository2.Get(ID, CountToFetch);
        }
        else if (DBSpecifier == 3)
        {
                return DuckbillItemsRepository3.Get(ID, CountToFetch);
        }
. . .
    }
}

public DuckbillItemRepository(int DBSpecifier)
{
    string id = string.Empty;

    try
    {
        if (DBSpecifier == 1)
       {
            using (var conn = new OleDbConnection(
                @"Provider=Microsoft.Jet.OLEDB.4.0;User ID=NRBQNRotPS;Password=NRBQNRotPS;Data Source=C:\PlatypusWin\DATA\PlatypusDAT01.MDB;Jet OLEDB:System database=C:\PlatypusWin\Data\NRBQ.mdw"))
       }
       else if (DBSpecifier == 2)
       {
            using (var conn = new OleDbConnection(
                @"Provider=Microsoft.Jet.OLEDB.4.0;User ID=NRBQNRotPS;Password=NRBQNRotPS;Data Source=C:\PlatypusWin\DATA\PlatypusDAT02.MDB;Jet OLEDB:System database=C:\PlatypusWin\Data\NRBQ.mdw"))
       }
       else if (DBSpecifier == 3)
       {
            using (var conn = new OleDbConnection(
                @"Provider=Microsoft.Jet.OLEDB.4.0;User ID=NRBQNRotPS;Password=NRBQNRotPS;Data Source=C:\PlatypusWin\DATA\PlatypusDAT03.MDB;Jet OLEDB:System database=C:\PlatypusWin\Data\NRBQ.mdw"))
       }
       . . .

return Repositories[DBSpecifier].Get(ID, CountToFetch);

using (var conn = new OleDbConnection(Repositories[DBSpecifier]))

?？当然不是，但是我怎么能攻击它呢

---

注：我知道使用MS Access是“有害的”；不过，我对此没有控制权/发言权。

在这两种情况下，我都会维护一个字典或列表，由DBSpecifier编制索引。这将避免所有if/elseif语句。如果DBSpecifier可以从0开始，那么我将使用一个列表，否则如果您想微观管理DBSpecifier值，我将使用字典

static readonly Dictionary<int, IDuckbillItemRepository> Repositories = new Dictionary<int, IDuckbillItemRepository> {
    { 1, new DuckbillItemRepository(1) },
    { 2, new DuckbillItemRepository(2) },
    { 3, new DuckbillItemRepository(3) }
};

同样，在存储库实现中：

static readonly Dictionary<int, string> ConnectionStrings = new Dictionary<int, string> {
    { 1, "@"Provider=Microsoft.Jet.OLEDB.4.0;...DAT01.MDB..." },
    { 2, "@"Provider=Microsoft.Jet.OLEDB.4.0;...DAT02.MDB..." },
    { 3, "@"Provider=Microsoft.Jet.OLEDB.4.0;...DAT03.MDB..." }
};

或者，为了避免重复，可以在静态构造函数的for循环中初始化字典项

您还可以使用dictionary.ContainsKey（DBSpecifier）对无效的DBSpecifier值执行错误检查

如果您想玩得开心，可以根据需要惰性地加载存储库字典，方法是检查字典是否包含具有给定DBSpecifier的键，如果尚未添加，则创建并添加新的存储库