（翻译）EntityFramework技巧系列之四-Tip13–15

1 ctx.Attach("Orders", order); 

1 ctx.Order.Attach(order);

1 void AttachToDefaultSet(T Entity); 

 1 public static EntityType GetCSpaceEntityType( 
 2        this MetadataWorkspace workspace 
 3 ) 
 4 { 
 5     if (workspace == null)  
 6         throw new ArgumentNullException("workspace"); 
 7     // Make sure the assembly for "T" is loaded 
 8     workspace.LoadFromAssembly(typeof(T).Assembly); 
 9     // Try to get the ospace type and if that is found 
10     // look for the cspace type too. 
11     EntityType ospaceEntityType = null; 
12     StructuralType cspaceEntityType = null; 
13     if (workspace.TryGetItem( 
14         typeof(T).FullName,  
15         DataSpace.OSpace, 
16         out ospaceEntityType)) 
17     { 
18         if (workspace.TryGetEdmSpaceType( 
19             ospaceEntityType, 
20             out cspaceEntityType)) 
21         { 
22             return cspaceEntityType as EntityType; 
23         } 
24     } 
25     return null; 
26 }

 1 public static IEnumerable GetHierarchy( 
 2     this EntityType entityType) 
 3 { 
 4     if (entityType == null) 
 5         throw new ArgumentNullException("entityType"); 
 6     while (entityType != null) 
 7     { 
 8         yield return entityType; 
 9         entityType = entityType.BaseType as EntityType; 
10     } 
11 }

 1 public static void AttachToDefaultSet( 
 2     this ObjectContext ctx,  
 3     T entity) 
 4 { 
 5     if (ctx== null) throw new ArgumentNullException("ctx"); 
 6     if (entity == null) throw new ArgumentNullException("entity"); 
 7 
 8   
 9     MetadataWorkspace wkspace = ctx.MetadataWorkspace; 
10     EntitySet set = wkspace 
11        .GetEntitySets(wkspace.GetCSpaceEntityType()) 
12        .Single(); 
13  
14     ctx.AttachTo(set.Name, entity); 
15 }

1 Product p = newProduct { ID = 1, Name = "Chocolate Fish" } ctx.AttachToDefaultSet(p);

 1 var customer = new Customer{ 
 2    Firstname = txtFirstname.Text, 
 3    Surname = txtSurname.Text, 
 4    Email = txtEmail.Text, 
 5    Street = txtStreet.Text, 
 6    City = txtCity.Text, 
 7    State = statesCache.GetSingle( 
 8       s => s.ID = Int32.Parse(ddState.SelectedValue) 
 9    ), 
10    Zip = txtZip.Text 
11 } 
12 ctx.AddToCustomers(customer); 
13 ctx.SaveChanges();

1 var state = statesCache.GetSingle( 
2      s => s.ID = Int32.Parse(ddState.SelectedValue) 
3 );
4 // See Tip 13 to avoid specifying the EntitySet 
5 // as a string 
6 ctx.AttachTo("States", s); 

 1 var customer = new Customer{ 
 2    Firstname = txtFirstname.Text, 
 3    Surname = txtSurname.Text, 
 4    Email = txtEmail.Text, 
 5    Street = txtStreet.Text, 
 6    City = txtCity.Text, 
 7    State = state, 
 8    Zip = txtZip.Text 
 9 } 
10 ctx.SaveChanges();

1 public State Clone(State state) 
2 { 
3    return new State {ID = state.ID}; 
4 }

1 var clOner= (State s) => new State {ID = s.ID};

 1 public class CloningCache where T : class 
 2 { 
 3     private List _innerData; 
 4     private Func _cloner; 
 5     public CloningCache(IEnumerable source, Func cloner) 
 6     { 
 7         _innerData = source.ToList(); 
 8         _clOner= cloner; 
 9     } 
10     public T GetSingle(Funcbool> predicate) 
11     { 
12         lock (_innerData) 
13         { 
14             return _innerData 
15                         .Where(predicate) 
16                         .Select(s => _cloner(s)) 
17                         .Single(); 
18         } 
19     } 
20 }

1 var statesCache = new CloningCache( 
2       ctx.States, 
3       (State s) => new State {ID = s.ID} 
4 );

1 var myPosts = from post in ctx.Posts  
2               orderby post.Created descending 
3               select post;

1 foreach(var post in myPosts) 
2 { 
3      Console.WriteLine("{0} on {1}", post.Title, post.Created); 
4 }

1 var myPosts = from post in ctx.Posts  
2               orderby post.Created descending 
3               select new {post.Title, post.Created};

 1 UPDATE [Table] 
 2 SET 
 3      ModifiedProperty1 = NewValue1, 
 4      ModifiedProperty2 = NewValue2, 
 5      ... 
 6      ModifiedPropertyN = NewValueN 
 7 WHERE 
 8      KeyProperty = KeyValue AND 
 9      ModifiedProperty1 = OriginalValue1 AND
10      ModifiedProperty2 = OriginalValue2 AND 
11      ... 
12      ModifiedPropertyN = OriginalValueN

 1 // Project just the columns we need 
 2 var myPosts = from post in ctx.Posts  
 3               orderby post.Created descending 
 4               select new {post.ID, post.Title};
 5 // Fabricate new Entities in memory. 
 6 // Notice the use of AsEnumerable() to separate the in db query 
 7 // from the LINQ to Objects construction of Post entities. 
 8 var fabricatedPosts = from p in myPosts.AsEnumerable() 
 9     select new Post{ID = p.ID, Title = post.Title};
10 // Now we attach the posts 
11 // And call a method to modify the Title 
12 foreach(var p in fabricatedPosts) 
13 { 
14     ctx.AttachTo("Posts", p); 
15     p.Title = ChangeTitle(p.Title); 
16 } 
17 ctx.SaveChanges();