There is no difference in deleting an entity in the connected and disconnected scenario in EF Core. EF Core made it easy to delete an entity from a context which in turn will delete a record in the database using the following methods. The following example demonstrates the different ways of deleting an entity in the disconnected scenario. In the above example, a Studnet entity with the valid StudentId is removed from a context using the Remove or RemoveRange method.
The data will be deleted from the database on SaveChanges. The above example executes the following delete command in the database:. Note: The DbContext. Remove and DbContext.
RemoveRange methods are newly introduced in EF Core to make the delete operation easy. If the Key value in the specified entity in the Remove or RemoveRange method does not exist in the corresponding database table, then EF Core will throw an exception: The following example will throw an exception. Database operation expected to affect 1 row s but actually affected 0 row s.
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Data may have been modified or deleted since entities were loaded. So, you need to handle the above exception appropriately or make sure that the corresponding data with id exists in the database before deleting it.
You can remove multiple entities in one go by using the DbContext. RemoveRange or DbSet.
RemoveRange method. The above example will delete 4 records from the database in a single database trip. Thus, EF Core improved the performance. If an entity has relationship with other entities such as one-to-one or one-to-many then deleting related data when the root entity is deleted is depends on how the relationship is configured.
For example, consider that the Student and Grade entities have a one-to-many relationship. There will be many student records for a particular GradeId.
EF will throw a reference integrity error if we try to delete a grade which has related Students records in the database. To solve this issue, you can define the referential constraint action options using Fluent API. For example, you can configure a cascade delete option for the relationship, as shown below.Optimistic vs Pessimistic Locking
Now, if you delete the Grade entity, then all the related Student records will also be deleted in the database. Remove DbSet. Remove Attaches the specified entity to the DbContext with Deleted state and starts tracking it.
The dark mode beta is finally here. Change your preferences any time. Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information. I'm working on a system that crawls data and stores them in a SQL Database, and as you can already guess the data is fed to the db only from a single source which is my application. However, there are cases where I need to overwrite old data without caring about any concurrency conflicts. I guess Entity Framework by default has some concurrency check mechanism in its kernel as it throws the following exception from time to time:.
As I mentioned previously, I really don't care about this and I just want to push data into the db. Is there any way to disable this in EF Core? To be clear, any way to define to the farmworker to just consider changes and push them in their place in the db? Learn more. Asked 1 year, 2 months ago.
Active 1 year, 2 months ago. Viewed times. I guess Entity Framework by default has some concurrency check mechanism in its kernel as it throws the following exception from time to time: Data may have been modified or deleted since entities were loaded As I mentioned previously, I really don't care about this and I just want to push data into the db.
Arrrr Arrrr 2, 1 1 gold badge 20 20 silver badges 44 44 bronze badges. AminSahranavard: Exactly the otherwise! EF defaults to no concurrency control last write wins which allows lost updates. The issue you are seeing is exactly what Amin mentioned: you loaded your entity from the db, then someone else deleted it or modified its primary key, and then, when you try to save, EF finds that no records are affected.
There is nothing to "overwrite". Active Oldest Votes. Sign up or log in Sign up using Google. Sign up using Facebook. Sign up using Email and Password.
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Entity Framework supports optimistic concurrency by default. EF saves an entity data to the database, assuming that the same data has not been changed since the entity was loaded.
If it finds that the data has changed, then an exception is thrown and you must resolve the conflict before attempting to save it again.
To handle concurrency using EF 6 database-first approach, create a column with rowversion timestamp data type in the table in the SQL Server. The rowversion synonym timestamp data type is just an incrementing binary number which is incremented for each insert and update operation performed on a table that contains a rowversion column. In order to check concurrency for the Student entity, the Student table must have a rowversion column.
So, create a new column named RowVersion in the Student table with timestamp datatype timestamp is synonym data type of rowversionas shown below:. You will see the RowVersion property added in the Student entity in the designer view. Now, you need to set the concurrency mode to fixed by right clicking on the RowVersion property of the Student entity on the designer, select Property and set Concurrency Mode to Fixed in the property window, as shown below:.
Assume that there are two users executing the above code. User1 and User2 both get the same Student entity. Now, User1 enters a new student name and saves it before User2. Entity Framework Courses on Pluralsight.GitHub is home to over 40 million developers working together to host and review code, manage projects, and build software together. Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community. Already on GitHub?
Sign in to your account. Concurrency check doesn't work when using RowVersion SQL Server's timestamp and one creates a new instance of byte array, instead of updating existing. See code below. EF Core version: 3. SqlServer works correctly with InMemory Target framework:. NET Core 3.
Problem with the current behaviour that it does not work with detached or mapped Entities over an API. ClientModel and Entity has a [TimeStamp]. So the concurrency does not work.
This is not the behaviour we expected. DerAlbertCom Yep, I ended up with doing something like that as well. You could use. DerAlbertCom MihaMarkic Would it be possible for one of you to put together a small, runnable project or complete code listing that shows why these workarounds are needed. I've read through the posts above several times and I'm not understanding what is going wrong here that would require mutating the array like this. I can only speak for myself, and i am using it in Unit Tests.
I am not testing database specifics, but how the rest of the infrastructure reacts on the occasion of such an exception. There are workarounds for this, or other ways to test, so its not an issue for us.
That being said, I would also be interested to see in what circumstances, outside of testing purposes, such manipulations would be useful. But, this is usefull in Application where it is possible that several People are working on the same Database Record. And in a szenario where the Data is serialized. Like an ASP. NET Core Application. Serialized in the. And if i have to serialize the RowVersion of the given DataRecord, i must be able to set the RowVersion on the entity.
Only with Updating the RowVersion byte by byte. EF Core works as expected. Or if we manually check the RowVersion.
Data Annotation - ConcurrencyCheck Attribute in EF 6 & EF Core
With your Workaround we have to select the entity twice if there was a change before the first select.Entity Framework Core implements optimistic concurrency strategy which is opposite to pessimistic concurrency strategy.
Lets's first clear out what are main differences between these two approaches in concurrency control. Optimistic concurrency control allows multiple processes to access and modify data without any explicit lock on the data. This increases performances significantly but opens the door to possible data concurrency which may cause data inconsistency and data overwriting.
In most of the cases you will not have to deal with concurrency issues. It is a part of good practice and something you need to implement to avoid these corner case situations. Pessimistic concurrency control performs explicit lock on the record that is edited and any other process that wants to edit the same record has to wait for the process that locked it to release it.
This approach is not so popular and used because it can make things complicated. You cannot keep the record locked for ever, so some lock timeout mechanism has to be in place and other things that initially impact performance downgrade as well as issues. Since EF Core implements optimistic concurrency control we will focus on that without going into the pessimistic concurrency control. This property is marked as a Timestamp field and it will be returned as byte array value once mapped from the table.
Since we will probably use this control for more than one table in our solution, it is a good practice to declare this property along with primary key in abstract class which will be inherited by every entity in your application.
All the classes that inherit BaseEntity will have the primary key Id GUID filed and Version field as concurrency token which will be checked on entity update. Timestamp will ensure that new value is generated and stored in the filed when record is created or updated. This way you can always compare only this field for the consistency instead of having to check all the properties of the entity for changes.
ConcurrencyCheck attribute will tell EF Core to check and compare values of the field to determine if there is a concurrency conflict. Now for the test purpose I created on sample entity which will inherit the base entity abstract class. This is pretty much you have to do to ensure data overwriting from different users of your application. EF Core will simply throw exception if concurrency happens. Now you also need to ensure that Version field value is transfered across all layers in your application.
I found base64 the most suitable way of doing this, so we eventually end up with two mappings for this purpose. If not present, EF Core will try to math empty value with the one present in database and you will not be able to update the entity because of DbUpdateConcurrencyException thwoen every time you try to update with empty Version field.
Optimistic Concurrency in Entity Framework Code First
You can return Bad request but I prefer to return Confilct as it is more descriptive because reason for the failure is data conflict. Resolving the data concurrency conflict. In he example above, we are not resolving the conflict programmatic in our code.I am the only user of my database at the moment, so I can guarantee that the data both exists and has not been changed outside the application!
Various forums have suggested that the way to deal with this is to set the column attributes so that the concurrency checking is disabled; i. However, to do this manually through the Visual Studio designer will take me hours I have a lot of tables and if I then change the schema of one of the tables in the DB, won't I then have to do it all again?
I've tried editing the. I've have had the same problem. I don't know of a quicker way. Thanks very much for the tip don't know why I didn't try that myself! Come to think of it, why isn't this the default? Why would you ever want it to be "Always" rather than "WhenChanged"?
Oh well -- it's working now, at least! Contrast with "WhenChanged", where if you don't touch it, it won't be checked; hence you could overwrite someone else's changes to that field by resetting it to its former value.
In fact, this should really be "Never", since if I ever want to change it for any reason it'll likely fail otherwise. Because the data could have been modified by another user or by some other process in your application.
If you use WhenChanged and your code doesn't change the property, it doesn't mean it hasn't been changed on the database. By using always you will make sure the data you are updating is the data you originally retrieved. How to turn off optimistic concurrency checking? Print Share Twitter Facebook Email. All suggestions gratefully received! Ed Graham. Draak Member. Re: How to turn off optimistic concurrency checking? Antony Highsky About Me. Thanks, Jonas -- I eventually came to the same conclusion myself.This page documents how concurrency works in EF Core and how to handle concurrency conflicts in your application.
See Concurrency Tokens for details on how to configure concurrency tokens in your model. You can view this article's sample on GitHub. Database concurrency refers to situations in which multiple processes or users access or change the same data in a database at the same time. Concurrency control refers to specific mechanisms used to ensure data consistency in presence of concurrent changes.
EF Core implements optimistic concurrency controlmeaning that it will let multiple processes or users make changes independently without the overhead of synchronization or locking. In the ideal situation, these changes will not interfere with each other and therefore will be able to succeed.
In the worst case scenario, two or more processes will attempt to make conflicting changes, and only one of them should succeed. Properties configured as concurrency tokens are used to implement optimistic concurrency control: whenever an update or delete operation is performed during SaveChangesthe value of the concurrency token on the database is compared against the original value read by EF Core.
The situation when another user has performed an operation that conflicts with the current operation is known as concurrency conflict. After executing the statements, EF Core reads the number of rows that were affected.
For example, we may want to configure LastName on Person to be a concurrency token. Continuing with the previous example, if one user tries to save some changes to a Personbut another user has already changed the LastNamethen an exception will be thrown.
At this point, the application could simply inform the user that the update was not successful due to conflicting changes and move on. But it may be desirable to prompt the user to ensure this record still represents the same actual person and to retry the operation. Resolving a concurrency conflict involves merging the pending changes from the current DbContext with the values in the database. What values get merged will vary based on the application and may be directed by user input.
There are three sets of values available to help resolve a concurrency conflict:. In the following example, Person. FirstName and Person. LastName are set up as concurrency tokens.