So LazyLoadingEnabled = false apparently doesn't do what I thought it did. And has next to no documentation.
I design my entity trees very carefully. I think hard about every relationship. When I load up an entity that is an Aggregate Root, I want everything that is navigable to from there to load. That's how the Aggregate root concept works after all, if I want something to be weekly related I'd stick an id on the entity and manage the relationship myself.
Is there a way to do this with Entity Framework?
You can try obtaining all NavigationProperties of the element type (in IQueryable). By accessing to the MetadataWorkspace of ObjectContext you can get those properties of a specific type and Include all easily.
Note that I suppose you're using EF5 or later version, whereas DbContext is used. We access to ObjectContext via the interface IObjectContextAdapter. Here is the code:
public static IQueryable<T> LoadAllRelatedObjects<T>(this IQueryable<T> source, DbContext context) {
//obtain the EntityType corresponding to the ElementType first
//then we can get all NavigationProperties of the ElementType
var items = (ObjectItemCollection) ((IObjectContextAdapter)context).ObjectContext.MetadataWorkspace.GetItemCollection(DataSpace.OSpace);
var entityType = items.OfType<EntityType>().Single(e => items.GetClrType(e) == source.ElementType);
return entityType.NavigationProperties
.Aggregate(source, (c, e) => c.Include(e.Name));
}
Note in new version (since EF5), the namespace of ObjectItemCollection (and other metadata items) is System.Data.Entity.Core.Metadata.Edm, while in the old version (before EF5), it's System.Data.Metadata.Emd.
Usage:
yourModel.YourEntities.LoadAllRelatedObjects(yourModel)
//. more query here ...
;
I don't think there's a way to have all of the navigation properties auto-eager load. How about making an extension method instead?
public static IQueryable<Company> LoadCompany(this IQueryable<Company> query) {
return query.Include(x => x.Divisions)
.Include(x => x.Departments)
.Include(x => x.Employees);
}
Example:
var query = from company in db.Companies.LoadCompany()
where company.Name == "Microsoft"
select company;
I'm using the newest Entity Framework and ran into a problem with Many To Many Relationship when I want to create an extra column.
The issue is the same raised in this older post:
EF Code First Additional column in join table for ordering purposes
Is it still the problem today that one can not add an extra column without loosing the many to many relation ship (link from object A to B as A.B because the mapping becomes and entity it self) ?
What are the work a rounds ?
Look up the a of class A I need and then query for mapping table where(e=>e.A == a) to get my Bs? And when I need the extra colums i would do MappingTable.find(a,b) ?
Are there other modeling options, linq to sql that would make it easier ?
As far as I know things haven't changed with EF 5. You would need to do it as the link says to. I like to stick with EF as its easy to use, but that's just my opinion...
I had the same problem. What I did to work-around it was create another derivative DbContext specifically to handle joins. I.E.:
public class JoinContext : DbContext
{
internal JoinContext() : base("name=SampleConnectionString")
{
PreventErrorIfDatabaseSchemaChanges();
// Get the ObjectContext related to this DbContext
var objectContext = (this as IObjectContextAdapter).ObjectContext;
}
public DbSet<StudentImage> StudentImages { get; set; }
protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
modelBuilder.Entity<StudentImage>()
.ToTable("StudentImages");
.HasKey(joinTable => new { joinTable.StudentId, joinTable.ImageId });
base.OnModelCreating(modelBuilder);
}
private static void PreventErrorIfDatabaseSchemaChanges()
{
Database.SetInitializer<JoinContext>(null);
}
}
I left the other application context with the Student/Image many-to-many join mapping as-is. Don't forget to specify a compounded key for the join table (refer to HasKey method above), else EF bombs on databse initialization.
After you have your special join context, use a repository to access this context and get or set the desired fields from mapped join table:
public class StudentRepository
{
public int GetImageSortOrder(int studentId, int imageId)
{
var joinContext = new JoinContext();
var joinTuple = joinContext.StudentImages.Find(studentId, imageId);
return joinTuple.SortOrder;
}
}
Hope this helps!
Below is my working table.
OrderID ProductID UnitPrice
1 P001 10
1 P002 11
1 P003 12
2 P001 10
I use below code to make delete every row(s) which orderID is 1.
void DeleteOrderMaster(int OrderID)
{
Order _Order = DB.Orders.SingleOrDefault(x => x.OrderID == OrderID);
DB.Orders.DeleteObject(_Order);
}
What my problem is about ...
ObjectContext.Table.DeleteObject(entity);
As I am not very familiar with DeleteObject function, I want to call that function like that
DeleteOrderMaster(1)
Please let me know is this correct way or not ?
ObjectContext.DeleteObject(object entity) method delete any entity that is not in detached state (object context is not set).
void DeleteOrderMaster(int OrderID)
{
Order _Order = DB.Orders.SingleOrDefault(x => x.OrderID == OrderID);
if(_Order!=null)
DB.DeleteObject(_Order);
}
Order _Order = DB.Orders.SingleOrDefault(x => x.OrderID == OrderID);
db.Orders.DeleteObject(_Order);
db.SaveChanges();
Remove is a method of DbSet class which can only be created from a DbContext class which is a part of Entity Framework.
EDIT
May be I confused myself, which as a result confused you. First of all apologies for that.
Now, coming back to explanation, you are indeed using the Entity Framework. The ObjectContext Class you mentioned and the DbContext class i referred both are parts of the Entity framework itself. The ObjectContext class lives in System.Data.Objects namespace whereas DbContext lives in the System.Data.Entity namespace.
Both ObjectContext and DbContext class provides facilities for querying and working with entity data as objects.
Now, When to use which one :-
Use ObjectContext for version 4.0 when using a designer generated model and DbContext with a 4.1 Code First model. Since you are using designer, I would say you go with ObjectContext.
Once again aplologies for the confusion. Hope, now I have given a better and complete answer
I want to delete several items from a table using Entity Framework. There is no foreign key / parent object, so I can't handle this with OnDeleteCascade.
Right now I'm doing this:
var widgets = context.Widgets
.Where(w => w.WidgetId == widgetId);
foreach (Widget widget in widgets)
{
context.Widgets.DeleteObject(widget);
}
context.SaveChanges();
It works, but the foreach bugs me. I'm using EF4, but I don't want to execute SQL. I just want to make sure I'm not missing anything -- this is as good as it gets, right? I can abstract the code with an extension method or helper, but somewhere we're still going to be doing a foreach, right?
EntityFramework 6 has made this a bit easier with .RemoveRange().
Example:
db.People.RemoveRange(db.People.Where(x => x.State == "CA"));
db.SaveChanges();
Warning! Do not use this on large datasets!
EF pulls all the data into memory, THEN deletes it. For smaller data sets this might not be an issue but generally avoid this style of delete unless you can guarantee you are only doing very small changes.
You could easily run your process out of memory while EF happily pulls in all the data you specified just to delete it.
using (var context = new DatabaseEntities())
{
context.ExecuteStoreCommand("DELETE FROM YOURTABLE WHERE CustomerID = {0}", customerId);
}
Addition: To support list of ids you can write
var listOfIds = String.Join(',',customerIds.Select(id => $"'{id}'").ToList());
var sql= $#"DELETE [YOURTABLE] WHERE CustomerID in ({listOfIds})";
Note: if CustomerID Is a string, you should double-check for potential SQL injection risks, for integer CustomerID it’s safe
this is as good as it gets, right? I can abstract it with an extension
method or helper, but somewhere we're still going to be doing a
foreach, right?
Well, yes, except you can make it into a two-liner:
context.Widgets.Where(w => w.WidgetId == widgetId)
.ToList().ForEach(context.Widgets.DeleteObject);
context.SaveChanges();
I know it's quite late but in case someone needs a simple solution, the cool thing is you can also add the where clause with it:
public static void DeleteWhere<T>(this DbContext db, Expression<Func<T, bool>> filter) where T : class
{
string selectSql = db.Set<T>().Where(filter).ToString();
string fromWhere = selectSql.Substring(selectSql.IndexOf("FROM"));
string deleteSql = "DELETE [Extent1] " + fromWhere;
db.Database.ExecuteSqlCommand(deleteSql);
}
Note: just tested with MSSQL2008.
Update:
The solution above won't work when EF generates sql statement with parameters, so here's the update for EF5:
public static void DeleteWhere<T>(this DbContext db, Expression<Func<T, bool>> filter) where T : class
{
var query = db.Set<T>().Where(filter);
string selectSql = query.ToString();
string deleteSql = "DELETE [Extent1] " + selectSql.Substring(selectSql.IndexOf("FROM"));
var internalQuery = query.GetType().GetFields(BindingFlags.NonPublic | BindingFlags.Instance).Where(field => field.Name == "_internalQuery").Select(field => field.GetValue(query)).First();
var objectQuery = internalQuery.GetType().GetFields(BindingFlags.NonPublic | BindingFlags.Instance).Where(field => field.Name == "_objectQuery").Select(field => field.GetValue(internalQuery)).First() as ObjectQuery;
var parameters = objectQuery.Parameters.Select(p => new SqlParameter(p.Name, p.Value)).ToArray();
db.Database.ExecuteSqlCommand(deleteSql, parameters);
}
It requires a little bit of reflection but works well.
If you don't want to execute SQL directly calling DeleteObject in a loop is the best you can do today.
However you can execute SQL and still make it completely general purpose via an extension method, using the approach I describe here.
Although that answer was for 3.5. For 4.0 I would probably use the new ExecuteStoreCommand API under the hood, instead of dropping down to the StoreConnection.
For anyone using EF5, following extension library can be used: https://github.com/loresoft/EntityFramework.Extended
context.Widgets.Delete(w => w.WidgetId == widgetId);
Entity Framework Core
3.1 3.0 2.2 2.1 2.0 1.1 1.0
using (YourContext context = new YourContext ())
{
var widgets = context.Widgets.Where(w => w.WidgetId == widgetId);
context.Widgets.RemoveRange(widgets);
context.SaveChanges();
}
Summary:
Removes the given collection of entities from the context underlying the set
with each entity being put into the Deleted state such that it will be deleted
from the database when SaveChanges is called.
Remarks:
Note that if System.Data.Entity.Infrastructure.DbContextConfiguration.AutoDetectChangesEnabled
is set to true (which is the default), then DetectChanges will be called once
before delete any entities and will not be called again. This means that in some
situations RemoveRange may perform significantly better than calling Remove multiple
times would do. Note that if any entity exists in the context in the Added state,
then this method will cause it to be detached from the context. This is because
an Added entity is assumed not to exist in the database such that trying to delete
it does not make sense.
Still seems crazy to have to pull anything back from the server just to delete it, but at least getting back just the IDs is a lot leaner than pulling down the full entities:
var ids = from w in context.Widgets where w.WidgetId == widgetId select w.Id;
context.Widgets.RemoveRange(from id in ids.AsEnumerable() select new Widget { Id = id });
Finally bulk delete has been introduced in Entity Framework Core 7 via the ExecuteDelete command:
context.Widgets
.Where(w => w.WidgetId == widgetId)
.ExecuteDelete();
Something to note here is that ExecuteDelete does not need a SaveChanges, as per its documentation:
This operation executes immediately against the database, rather than being deferred until DbContext.SaveChanges() is called. It also does not interact with the EF change tracker in any way: entity instances which happen to be tracked when this operation is invoked aren't taken into account, and aren't updated to reflect the changes.
I know that the question was asked for EF4, but if you upgrade this is a good alternative!
EF 6.1
public void DeleteWhere<TEntity>(Expression<Func<TEntity, bool>> predicate = null)
where TEntity : class
{
var dbSet = context.Set<TEntity>();
if (predicate != null)
dbSet.RemoveRange(dbSet.Where(predicate));
else
dbSet.RemoveRange(dbSet);
context.SaveChanges();
}
Usage:
// Delete where condition is met.
DeleteWhere<MyEntity>(d => d.Name == "Something");
Or:
// delete all from entity
DeleteWhere<MyEntity>();
For EF 4.1,
var objectContext = (myEntities as IObjectContextAdapter).ObjectContext;
objectContext.ExecuteStoreCommand("delete from [myTable];");
The quickest way to delete is using a stored procedure. I prefer stored procedures in a database project over dynamic SQL because renames will be handled correctly and have compiler errors. Dynamic SQL could refer to tables that have been deleted/renamed causing run time errors.
In this example, I have two tables List and ListItems. I need a fast way to delete all the ListItems of a given list.
CREATE TABLE [act].[Lists]
(
[Id] INT NOT NULL PRIMARY KEY IDENTITY,
[Name] NVARCHAR(50) NOT NULL
)
GO
CREATE UNIQUE INDEX [IU_Name] ON [act].[Lists] ([Name])
GO
CREATE TABLE [act].[ListItems]
(
[Id] INT NOT NULL IDENTITY,
[ListId] INT NOT NULL,
[Item] NVARCHAR(100) NOT NULL,
CONSTRAINT PK_ListItems_Id PRIMARY KEY NONCLUSTERED (Id),
CONSTRAINT [FK_ListItems_Lists] FOREIGN KEY ([ListId]) REFERENCES [act].[Lists]([Id]) ON DELETE CASCADE
)
go
CREATE UNIQUE CLUSTERED INDEX IX_ListItems_Item
ON [act].[ListItems] ([ListId], [Item]);
GO
CREATE PROCEDURE [act].[DeleteAllItemsInList]
#listId int
AS
DELETE FROM act.ListItems where ListId = #listId
RETURN 0
Now the interesting part of deleting the items and updating Entity framework using an extension.
public static class ListExtension
{
public static void DeleteAllListItems(this List list, ActDbContext db)
{
if (list.Id > 0)
{
var listIdParameter = new SqlParameter("ListId", list.Id);
db.Database.ExecuteSqlCommand("[act].[DeleteAllItemsInList] #ListId", listIdParameter);
}
foreach (var listItem in list.ListItems.ToList())
{
db.Entry(listItem).State = EntityState.Detached;
}
}
}
The main code can now use it is as
[TestMethod]
public void DeleteAllItemsInListAfterSavingToDatabase()
{
using (var db = new ActDbContext())
{
var listName = "TestList";
// Clean up
var listInDb = db.Lists.Where(r => r.Name == listName).FirstOrDefault();
if (listInDb != null)
{
db.Lists.Remove(listInDb);
db.SaveChanges();
}
// Test
var list = new List() { Name = listName };
list.ListItems.Add(new ListItem() { Item = "Item 1" });
list.ListItems.Add(new ListItem() { Item = "Item 2" });
db.Lists.Add(list);
db.SaveChanges();
listInDb = db.Lists.Find(list.Id);
Assert.AreEqual(2, list.ListItems.Count);
list.DeleteAllListItems(db);
db.SaveChanges();
listInDb = db.Lists.Find(list.Id);
Assert.AreEqual(0, list.ListItems.Count);
}
}
You can use extensions libraries for doing that like EntityFramework.Extended or Z.EntityFramework.Plus.EF6, there are available for EF 5, 6 or Core. These libraries have great performance when you have to delete or update and they use LINQ. Example for deleting (source plus):
ctx.Users.Where(x => x.LastLoginDate < DateTime.Now.AddYears(-2))
.Delete();
or (source extended)
context.Users.Where(u => u.FirstName == "firstname")
.Delete();
These use native SQL statements, so performance is great.
This answers is for EF Core 7 (I am not aware if they merged EF Core with EF now or not, before they kept the two separately).
EF Core 7 now supports ExecuteUpdate and ExecuteDelete (Bulk updates):
// Delete all Tags (BE CAREFUL!)
await context.Tags.ExecuteDeleteAsync();
// Delete Tags with a condition
await context.Tags.Where(t => t.Text.Contains(".NET")).ExecuteDeleteAsync();
The equivalent SQL queries are:
DELETE FROM [t]
FROM [Tags] AS [t]
DELETE FROM [t]
FROM [Tags] AS [t]
WHERE [t].[Text] LIKE N'%.NET%'
If you want to delete all rows of a table, you can execute sql command
using (var context = new DataDb())
{
context.Database.ExecuteSqlCommand("TRUNCATE TABLE [TableName]");
}
TRUNCATE TABLE (Transact-SQL) Removes all rows from a table without logging the individual row deletions. TRUNCATE TABLE is similar to the DELETE statement with no WHERE clause; however, TRUNCATE TABLE is faster and uses fewer system and transaction log resources.
You can execute sql queries directly as follows :
private int DeleteData()
{
using (var ctx = new MyEntities(this.ConnectionString))
{
if (ctx != null)
{
//Delete command
return ctx.ExecuteStoreCommand("DELETE FROM ALARM WHERE AlarmID > 100");
}
}
return 0;
}
For select we may use
using (var context = new MyContext())
{
var blogs = context.MyTable.SqlQuery("SELECT * FROM dbo.MyTable").ToList();
}
UUHHIVS's is a very elegant and fast way for batch delete, but it must be used with care:
auto generation of transaction: its queries will be encompassed by a transaction
database context independence: its execution has nothing to do with context.SaveChanges()
These issues can be circumvented by taking control of the transaction. The following code illustrates how to batch delete and bulk insert in a transactional manner:
var repo = DataAccess.EntityRepository;
var existingData = repo.All.Where(x => x.ParentId == parentId);
TransactionScope scope = null;
try
{
// this starts the outer transaction
using (scope = new TransactionScope(TransactionScopeOption.Required))
{
// this starts and commits an inner transaction
existingData.Delete();
// var toInsert = ...
// this relies on EntityFramework.BulkInsert library
repo.BulkInsert(toInsert);
// any other context changes can be performed
// this starts and commit an inner transaction
DataAccess.SaveChanges();
// this commit the outer transaction
scope.Complete();
}
}
catch (Exception exc)
{
// this also rollbacks any pending transactions
scope?.Dispose();
}
In EF 7 you can use bulk delete
var ids = widgets.Select(x => x.Id).ToList();
await _mrVodDbContext.Widgets.Where(x => ids.Contains(x.Id)).ExecuteDeleteAsync();
EF core generate
DELETE FROM [i]
FROM [Widgets] AS [i]
WHERE [i].[Id] IN (4,3,2,1)
More about deleting or updating in release notes. https://learn.microsoft.com/en-us/ef/core/what-is-new/ef-core-7.0/whatsnew#basic-executedelete-examples
You can also use the DeleteAllOnSubmit() method by passing it your results in a generic list rather than in var. This way your foreach reduces to one line of code:
List<Widgets> widgetList = context.Widgets
.Where(w => w.WidgetId == widgetId).ToList<Widgets>();
context.Widgets.DeleteAllOnSubmit(widgetList);
context.SubmitChanges();
It probably still uses a loop internally though.
Thanh's answer worked best for me. Deleted all my records in a single server trip. I struggled with actually calling the extension method, so thought I would share mine (EF 6):
I added the extension method to a helper class in my MVC project and changed the name to "RemoveWhere". I inject a dbContext into my controllers, but you could also do a using.
// make a list of items to delete or just use conditionals against fields
var idsToFilter = dbContext.Products
.Where(p => p.IsExpired)
.Select(p => p.ProductId)
.ToList();
// build the expression
Expression<Func<Product, bool>> deleteList =
(a) => idsToFilter.Contains(a.ProductId);
// Run the extension method (make sure you have `using namespace` at the top)
dbContext.RemoveWhere(deleteList);
This generated a single delete statement for the group.
I came up with a great library Zack.EFCore.Batch. It will convert your expression into simple DELETE FROM .... WHERE query. (Like some answers proposed) https://github.com/yangzhongke/Zack.EFCore.Batch
The usage example:
await ctx.DeleteRangeAsync<Book>(b => b.Price > n);
The Zack.EFCore.Batch library has lots of benefits over Z.EntityFramework.Extended https://entityframework-extensions.net/ which does not have true Async methods. (They are just wrappers around sync methods) You can get lots of unexpected issues by using this library in high load environment.
EF 6.=>
var assignmentAddedContent = dbHazirBot.tbl_AssignmentAddedContent.Where(a =>
a.HazirBot_CategoryAssignmentID == categoryAssignment.HazirBot_CategoryAssignmentID);
dbHazirBot.tbl_AssignmentAddedContent.RemoveRange(assignmentAddedContent);
dbHazirBot.SaveChanges();
Best : in EF6 => .RemoveRange()
Example:
db.Table.RemoveRange(db.Table.Where(x => Field == "Something"));
If you are using Generic Repository:
Inside Generic repository, following could be new method.
public void RemoveMultiple(Expression<Func<T, bool>> predicate)
{
IQueryable<T> query = _context.Set<T>().Where(predicate);
_context.Set<T>().RemoveRange(query.AsNoTracking());
}
Usage:
_unitOfWork.YOUR_ENTITY.RemoveMultiple(x => x.AccountId == accountId);
_unitOfWork.Complete();
context.Widgets.RemoveRange(context.Widgets.Where(w => w.WidgetId == widgetId).ToList());
db.SaveChanges();
See the answer 'favorite bit of code' that works
Here is how I used it:
// Delete all rows from the WebLog table via the EF database context object
// using a where clause that returns an IEnumerable typed list WebLog class
public IEnumerable<WebLog> DeleteAllWebLogEntries()
{
IEnumerable<WebLog> myEntities = context.WebLog.Where(e => e.WebLog_ID > 0);
context.WebLog.RemoveRange(myEntities);
context.SaveChanges();
return myEntities;
}
In EF 6.2 this works perfectly, sending the delete directly to the database without first loading the entities:
context.Widgets.Where(predicate).Delete();
With a fixed predicate it's quite straightforward:
context.Widgets.Where(w => w.WidgetId == widgetId).Delete();
And if you need a dynamic predicate have a look at LINQKit (Nuget package available), something like this works fine in my case:
Expression<Func<Widget, bool>> predicate = PredicateBuilder.New<Widget>(x => x.UserID == userID);
if (somePropertyValue != null)
{
predicate = predicate.And(w => w.SomeProperty == somePropertyValue);
}
context.Widgets.Where(predicate).Delete();