基於可選搜索參數使用實體框架選擇數據

Question

我有一個使用EF與數據庫接口的項目。它通過WCF Web服務完成此操作。這是我的第一個EF項目，我正在努力研究如何構建基於可選參數的查詢。

我的web服務有一個數據協定，其中包含與EF中的類匹配的字段。 Web服務提供數據庫服務，填充這些客戶端類並將其傳遞迴客戶端。舉一個例子....

在web服務

[DataContract] 
public class MyMovie 
{ 
    [DataMember] 
    public int MovieId; 
    [DataMember] 
    public string MovieName; 
    [DataMember] 
    public int MovieRatingId; 
    [DataMember] 
    public string MovieRunTime; 
    [DataMember] 
    public string MovieIMDBUrl; 
    [DataMember] 
    public DateTime MovieDateAdded; 
    [DataMember] 
    public List<MyMovieActor> Actors; 
    [DataMember] 
    public List<MyMovieMedia> MediaFiles; 
} 
public class MyMovieActor 
{ 
    [DataMember] 
    public int ActorId; 
    [DataMember] 
    public int ActorMovieId; 
    [DataMember] 
    public string ActorName; 
    [DataMember] 
    public string ActorCharacter; 
} 
public class MyMovieMedia 
{ 
    [DataMember] 
    public int MediaId; 
    [DataMember] 
    public int MediaMovieId; 
    [DataMember] 
    public string MediaFileLocation; 
    [DataMember] 
    public bool MediaDefault; 
} 

數據模型（簡化的）...

我的web服務方法....

public MyMovie GetMovie(int movieId) 
    { 
     MyMovie response = new MyMovie(); 

     using (MovieDatabaseEntities DbContext = new MovieDatabaseEntities()) 
     { 
      var query = (from oData in DbContext.Movies 
         where oData.MovieId == movieId 
         select oData).ToList(); 


      if (query.Count > 0) 
      { 
       response.MovieDateAdded = query[0].MovieDateAdded; 
       response.MovieId = query[0].MovieId; 
       response.MovieIMDBUrl = query[0].MovieIMDBUrl; 
       response.MovieName = query[0].MovieName; 
       response.MovieRatingId = query[0].MovieRatingId; 
       response.MovieRunTime = query[0].MovieRunTime; 
      } 

      List<MyMovieActor> actors = new List<MyMovieActor>(); 
      foreach (MovieActor ma in query[0].MovieActors) 
      { 
       MyMovieActor a = new MyMovieActor(); 
       a.ActorId = ma.ActorId; 
       a.ActorMovieId = ma.ActorMovieId; 
       a.ActorCharacter = ma.ActorCharacter; 
       a.ActorName = ma.ActorName; 
       actors.Add(a); 
      } 
      response.Actors = actors; 

      List<MyMovieMedia> medias = new List<MyMovieMedia>(); 
      foreach (MovieMedia mm in query[0].MovieMedias) 
      { 
       MyMovieMedia med = new MyMovieMedia(); 
       med.MediaId = mm.MediaId; 
       med.MediaMovieId = mm.MediaMovieId; 
       med.MediaFileLocation = mm.MediaFileLocation; //HDD Folder 
       med.MediaDefault = mm.MediaDefault; //Image to show on listing 
       medias.Add(med); 
      } 
      response.MediaFiles = medias; 
     } 
     return response; 
    } 

所以現在我想創建

public List<MyMovie> GetMovies(string moviename, int movierating, string movieruntime) 

其中將填充所有參數或零長度字符串。如果他們有一個值，我想添加它作爲where子句的一部分。

所以基本上更新

   var query = (from oData in DbContext.Movies 
         where oData.MovieId == movieId 
         select oData).ToList(); 

到

  var query = (from oData in DbContext.Movies 
         where 1=1 
        if(String.IsSafe(moviename)) 
        { 
         && oData.MovieName Like %movieId% 
        } 
        if(movierating != 0) 
        { 
         && oData.MovieRating = movierating 
        } 
        if(String.IsSafe(movieruntime)) 
        { 
         && oData.MovieRuntime == movieruntime 
        } 
         select oData).ToList(); 

相當於展望這個剛剛困惑我更多，我一直用好老ADO.NET，的DataReader writen我的數據層，適配器，存儲過程等，但在這個項目中，我被要求使用EF。這讓我很困惑。他們怎麼說老狗和新花樣？

任何與此有關的幫助將非常感激。

Answer 1

IQueryable是你的朋友在這裏。它允許在多個步驟中組合查詢，但它不會生成SQL並在需要之前執行它（例如由於迭代或ToList（）調用）。所以你的代碼看起來像：

var query = (from oData in DbContext.Movies select oData); 
if (!string.IsNullOrEmpty(moviename)) 
    query = query.Where(m => m.MovieName.Contains(moviename)); 
...