When a new Post is input into the system, a number of Tags will need to be instantiated and associated with the Post instance. Some of these Tags will already exist in the db, others will not and will need inserting.
An example:
var post = new Post {
Slug = "hello-world",
Title = "Hello, World!",
Content = "this is my first post.",
Tags = new List<Tag>()
};
var tag = new Tag { Name = "introduction" };
post.Tags.Add(tag);
When an associated Tag does not exist in the db, I can rely on a simple call to DbSet<T>.Add to insert both the post and the associated tags into the db.
However, attempting to insert a post with associated tags that already exist in the db causes a primary key violation on the tags table.
In an attempt to solve this problem, I tried to Attach each tag to the database context which works super when the tags already exist in the database but otherwise, an exception is thrown with the following inner exception:
The INSERT statement conflicted with the FOREIGN KEY constraint "FK_dbo.TagPosts_dbo.Tags_Tag_Name". The conflict occurred in
database "EF.Domain.BlogDb", table "dbo.Tags", column
'Name'. The statement has been terminated."}
I want to insert tags associated with the post into the database only when it is required. How can I achieve this?
Your predicament is quite interesting. If you wouldn't use a generic repository but a specific repository that knows the primary key of the entity you want to attach is you could just use a code like this:
var tagExists = Tags.Any(t => t.Name == tag.Name);
or
var tag = Tags.Find(tag.Name);
however in your case we need a more general approach such as getting the primary key of the entity the Repository class uses regardless the type of the entity. To achieve this I've created two extension methods on the DbContext class:
public static IList<string> GetPrimaryKeyNames<TEntity>(this DbContext context)
where TEntity : class
{
var objectContext = ((IObjectContextAdapter)context).ObjectContext;
var set = objectContext.CreateObjectSet<TEntity>();
return set.EntitySet.ElementType
.KeyMembers
.Select(k => k.Name)
.ToList();
}
public static IList<object> GetPrimaryKeyValues<TEntity>(this DbContext context, TEntity entity)
where TEntity : class
{
var valueList = new List<object>();
var primaryKeyNames = context.GetPrimaryKeyNames<TEntity>();
foreach(var propertyInfo in entity.GetType().GetProperties())
{
if (primaryKeyNames.Contains(propertyInfo.Name))
{
valueList.Add(propertyInfo.GetValue(entity));
}
}
return valueList;
}
Utilizing these methods you can change the Attach method on the Repository class like the following:
public void Attach(TEntity entity)
{
var storeEntity = _context.Set<TEntity>().Find(
_context.GetPrimaryKeyValues(entity).ToArray());
if (storeEntity != null)
{
_context.Entry(storeEntity).State = EntityState.Detached;
_context.Set<TEntity>().Attach(entity);
}
}
Our project is currently migrating to EF(and away from Stored Procs), and one of the enhancements(we're adding to the architecture) is using Optimistic Concurrency when users save data to the database(we currently don't have this feature). I'm having problems getting EF to fail when it should. In other words when two users open the same record, each make changes and attempts to save those changes the first to save update the record, and the second would get an error message. I created a simple example to illustrate my problem.
In the database I have the following table(and insert test data):
Create Table Work
(
Id int identity(1,1) Primary Key
,UserIdAssignTo int null
,RowVer RowVersion not null
)
Insert Into Work(UserIdAssignTo)Values(1)
I created an EF file (.edmx) and drag/drop the table, above, onto the canvas. I updated the properties on the property/column RowVer as follows:
RowVer Property/Column
Concurrency Mode: Fixed
Getter/Setter are both Public
Nullable: False
Store Generated: Computed
Type: Binary
I have an object that will retrieve and update the table like below:
public class Work
{
public int Id { get; set; }
public int? UserIdAssignTo { get; set; }
public byte[] Version { get; set; }
private string _conn = String.Empty;
public WorkData()
{
_conn = GetConnectionsString();
}
public void GetById(int WorkID)
{
using (SQL context = new SQL(_conn))
{
Work fromDb = context.Works.FirstOrDefault(db => db.Id == WorkID);
if (fromDb != null)
{
Id = fromDb.Id;
UserIdAssignTo = fromDb.UserIdAssignTo;
Version = fromDb.RowVer;
}
}
}
public void Update()
{
using (SQL context = new SQL(_conn))
{
Work fromDb = context.Works.FirstOrDefault(db => db.Id == Id);
if (fromDb != null)
{
fromDb.UserIdAssignTo = UserIdAssignTo;
fromDb.RowVer = Version;
context.SaveChanges();
UserIdAssignTo = fromDb.UserIdAssignTo;
Version = fromDb.RowVer;
}
}
}
}
I developed a test case to expose the error I'm getting:
[Test]
public void ConcurencyDataTest()
{
WorkData first = new WorkData();
first.GetById(1);
WorkData second = new WorkData();
second.GetById(1);
first.UserIdAssignTo = null;
first.Update();
second.UserIdAssignTo = 1;
second.Update(); // I should get an exception b/c the object is outdated
}
After both "first" and "second" object call the GetById(1) method, their RowVer property is the same for both objects(as expected).
I ran SQL profiler when I executed this test
The below is when the "first" object called Update method
exec sp_executesql N'update [dbo].[Work]
set [UserIdAssignTo] = null
where (([Id] = #0) and ([RowVer] = #1))
select [RowVer]
from [dbo].[Work]
where ##ROWCOUNT > 0 and [Id] = #0',N'#0 int,#1 binary(8)',#0=1,#1=0x00000000024E6E2
Note the #1 parameter, both the "first" and "second" object should have that in memory and use it when update
When second.Update was called, the SQL profiler recorded this:
exec sp_executesql N'update [dbo].[Work]
set [UserIdAssignTo] = #0
where (([Id] = #1) and ([RowVer] = #2))
select [RowVer]
from [dbo].[Work]
where ##ROWCOUNT > 0 and [Id] = #1',N'#0 int,#1 int,#2 binary(8)',#0=1,#1=1,#2=0x00000000024E6E2F
Note the #1 parameter has changed to the new value(after "first" updated), when it should be the old value that was held by the object "second"(the old value is 0x00000000024E6E2). I don't understand how it got changed and I'm a little confused on how to properly implement first write concurrency through EF.
The results I'm actually getting is the "second" object is successfully updating the table, when it should be failing.
Edit: This to simulate using an N-tier architecture. I'm trying to update with detached objects.
I think it is because in your update method you retrieve the object again from the context which would get the current value of RowVer. Since it is computed I don't think setting it back to the previous version would work. So when it updates it does have the current value of RowVer that is in the table.
I think you instead would need to attach or add the object to the context.
http://msdn.microsoft.com/en-us/library/bb896271.aspx
http://blogs.msdn.com/b/adonet/archive/2011/01/29/using-dbcontext-in-ef-feature-ctp5-part-4-add-attach-and-entity-states.aspx
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();