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ExecuteUpdate and ExecuteDelete

  • Článok

Note

This feature was introduced in EF Core 7.0.

ExecuteUpdate and ExecuteDelete are a way to save data to the database without using EF's traditional change tracking and SaveChanges() method. For an introductory comparison of these two techniques, see the Overview page on saving data.

ExecuteDelete

Let's assume that you need to delete all Blogs with a rating below a certain threshold. The traditional SaveChanges() approach requires you to do the following:

foreach (var blog in context.Blogs.Where(b => b.Rating < 3))
{
    context.Blogs.Remove(blog);
}

context.SaveChanges();

This is quite an inefficient way to perform this task: we query the database for all Blogs matching our filter, and then we query, materialize and track all those instances; the number of matching entities could be huge. We then tell EF's change tracker that each Blog needs to be removed, and apply those changes by calling SaveChanges(), which generates a DELETE statement for each and every one of them.

Here is the same task performed via the ExecuteDelete API:

context.Blogs.Where(b => b.Rating < 3).ExecuteDelete();

This uses the familiar LINQ operators to determine which Blogs should be affected - just as if we were querying them - and then tells EF to execute a SQL DELETE against the database:

DELETE FROM [b]
FROM [Blogs] AS [b]
WHERE [b].[Rating] < 3

Aside from being simpler and shorter, this executes very efficiently in the database, without loading any data from the database or involving EF's change tracker. Note that you can use arbitrary LINQ operators to select which Blogs you'd like to delete - these are translated to SQL for execution at the database, just as if you were querying those Blogs out.

ExecuteUpdate

Rather than deleting these Blogs, what if we wanted to change a property to indicate that they should be hidden instead? ExecuteUpdate provides a similar way to express a SQL UPDATE statement:

context.Blogs
    .Where(b => b.Rating < 3)
    .ExecuteUpdate(setters => setters.SetProperty(b => b.IsVisible, false));

Like with ExecuteDelete, we first use LINQ to determine which Blogs should be affected; but with ExecuteUpdate we also need to express the change to be applied to the matching Blogs. This is done by calling SetProperty within the ExecuteUpdate call, and providing it with two arguments: the property to be changed (IsVisible), and the new value it should have (false). This causes the following SQL to be executed:

UPDATE [b]
SET [b].[IsVisible] = CAST(0 AS bit)
FROM [Blogs] AS [b]
WHERE [b].[Rating] < 3

Updating multiple properties

ExecuteUpdate allows updating multiple properties in a single invocation. For example, to both set IsVisible to false and to set Rating to zero, simply chain additional SetProperty calls together:

context.Blogs
    .Where(b => b.Rating < 3)
    .ExecuteUpdate(setters => setters
        .SetProperty(b => b.IsVisible, false)
        .SetProperty(b => b.Rating, 0));

This executes the following SQL:

UPDATE [b]
SET [b].[Rating] = 0,
    [b].[IsVisible] = CAST(0 AS bit)
FROM [Blogs] AS [b]
WHERE [b].[Rating] < 3

Referencing the existing property value

The above examples updated the property to a new constant value. ExecuteUpdate also allows referencing the existing property value when calculating the new value; for example, to increase the rating of all matching Blogs by one, use the following:

context.Blogs
    .Where(b => b.Rating < 3)
    .ExecuteUpdate(setters => setters.SetProperty(b => b.Rating, b => b.Rating + 1));

Note that the second argument to SetProperty is now a lambda function, and not a constant as before. Its b parameter represents the Blog being updated; within that lambda, b.Rating thus contains the rating before any change occurred. This executes the following SQL:

UPDATE [b]
SET [b].[Rating] = [b].[Rating] + 1
FROM [Blogs] AS [b]
WHERE [b].[Rating] < 3

ExecuteUpdate does not currently support referencing navigations within the SetProperty lambda. For example, let's say we want to update all the Blogs' ratings so that each Blog's new rating is the average of all its Posts' ratings. We may try to use ExecuteUpdate as follows:

context.Blogs.ExecuteUpdate(
    setters => setters.SetProperty(b => b.Rating, b => b.Posts.Average(p => p.Rating)));

However, EF does allow performing this operation by first using Select to calculate the average rating and project it to an anonymous type, and then using ExecuteUpdate over that:

context.Blogs
    .Select(b => new { Blog = b, NewRating = b.Posts.Average(p => p.Rating) })
    .ExecuteUpdate(setters => setters.SetProperty(b => b.Blog.Rating, b => b.NewRating));

This executes the following SQL:

UPDATE [b]
SET [b].[Rating] = CAST((
    SELECT AVG(CAST([p].[Rating] AS float))
    FROM [Post] AS [p]
    WHERE [b].[Id] = [p].[BlogId]) AS int)
FROM [Blogs] AS [b]

Change tracking

Users familiar with SaveChanges are used to performing multiple changes, and then calling SaveChanges to apply all these changes to the database; this is made possible by EF's change tracker, which accumulates - or tracks - these changes.

ExecuteUpdate and ExecuteDelete work quite differently: they take effect immediately, at the point in which they are invoked. This means that while a single ExecuteUpdate or ExecuteDelete operation can affect many rows, it isn't possible to accumulate multiple such operations and apply them at once, e.g. when calling SaveChanges. In fact, the functions are completely unaware of EF's change tracker, and have no interaction with it whatsoever. This has several important consequences.

Consider the following code:

// 1. Query the blog with the name `SomeBlog`. Since EF queries are tracking by default, the Blog is now tracked by EF's change tracker.
var blog = context.Blogs.Single(b => b.Name == "SomeBlog");

// 2. Increase the rating of all blogs in the database by one. This executes immediately.
context.Blogs.ExecuteUpdate(setters => setters.SetProperty(b => b.Rating, b => b.Rating + 1));

// 3. Increase the rating of `SomeBlog` by two. This modifies the .NET `Rating` property and is not yet persisted to the database.
blog.Rating += 2;

// 4. Persist tracked changes to the database.
context.SaveChanges();

Crucially, when ExecuteUpdate is invoked and all Blogs are updated in the database, EF's change tracker is not updated, and the tracked .NET instance still has its original rating value, from the point at which it was queried. Let's assume that the Blog's rating was originally 5; after the 3rd line executes, the rating in the database is now 6 (because of the ExecuteUpdate), whereas the rating in the tracked .NET instance is 7. When SaveChanges is called, EF detects that the new value 7 is different from the original value 5, and persists that change. The change performed by ExecuteUpdate is overwritten and not taken into account.

As a result, it is usually a good idea to avoid mixing both tracked SaveChanges modifications and untracked modifications via ExecuteUpdate/ExecuteDelete.

Transactions

Continuing on the above, it's important to understand that ExecuteUpdate and ExecuteDelete do not implicitly start a transaction they're invoked. Consider the following code:

context.Blogs.ExecuteUpdate(/* some update */);
context.Blogs.ExecuteUpdate(/* another update */);

var blog = context.Blogs.Single(b => b.Name == "SomeBlog");
blog.Rating += 2;
context.SaveChanges();

Each ExecuteUpdate call causes a single SQL UPDATE to be sent to the database. Since no transaction is created, if any sort of failure prevents the second ExecuteUpdate from completing successfully, the effects of the first one are still persisted to the database. In fact, the four operations above - two invocations of ExecuteUpdate, a query and SaveChanges - each executes within its own transaction. To wrap multiple operations in a single transaction, explicitly start a transaction with DatabaseFacade:

using (var transaction = context.Database.BeginTransaction())
{
    context.Blogs.ExecuteUpdate(/* some update */);
    context.Blogs.ExecuteUpdate(/* another update */);

    ...
}

For more information about transaction handling, see Using Transactions.

Concurrency control and rows affected

SaveChanges provides automatic Concurrency Control, using a concurrency token to ensure that a row wasn't changed between the moment you loaded it and the moment you save changes to it. Since ExecuteUpdate and ExecuteDelete do not interact with the change tracker, they cannot automatically apply concurrency control.

However, both these methods do return the number of rows that were affected by the operation; this can come particularly handy for implementing concurrency control yourself:

// (load the ID and concurrency token for a Blog in the database)

var numUpdated = context.Blogs
    .Where(b => b.Id == id && b.ConcurrencyToken == concurrencyToken)
    .ExecuteUpdate(/* ... */);
if (numUpdated == 0)
{
    throw new Exception("Update failed!");
}

In this code, we use a LINQ Where operator to apply an update to a specific Blog, and only if its concurrency token has a specific value (e.g. the one we saw when querying the Blog from the database). We then check how many rows were actually updated by ExecuteUpdate; if the result is zero, no rows were updated and the concurrency token was likely changed as a result of a concurrent update.

Limitations

  • Only updating and deleting is currently supported; insertion must be done via DbSet<TEntity>.Add and SaveChanges().
  • While the SQL UPDATE and DELETE statements allow retrieving original column values for the rows affected, this isn't currently supported by ExecuteUpdate and ExecuteDelete.
  • Multiple invocations of these methods cannot be batched. Each invocation performs its own roundtrip to the database.
  • Databases typically allow only a single table to be modified with UPDATE or DELETE.
  • These methods currently only work with relational database providers.

Additional resources