Find foreign key references in EF Core-CodePudding

The short version:

Is there a way to ask Entity Framework Core 7 (EF Core 7) if a generic entity has any Foreign Key (FK) references? Put another way, is there a way to ask EF Core 7 if deleting an entity would fail due to an FK reference violation (assuming all FK references are NOT cascade deletes)?

The long version:

I have a website that sells widgets. The website contains a SQL database and uses EF Core 7 to access the database.

The database contains several tables that contain information about things that don't change often, such as widget descriptions, tax schedules, etc. These tables are referenced by many other tables (orders, shipping, product support, etc.). Thus, rows in these "don't change very often" tables cannot be deleted if any of the other tables (orders, shipping, etc.) have FK references to them. Put another way, you can't delete a widget if the shipping table thinks that that type of widget is on a truck heading to Omaha.

When I want to update my list of widgets (or my tax schedules, or any of the "don't change very often" tables), I call a generic function that accepts the up-to-date List of generic entities, and updates the database, adding, updating, or deleting items in the database as necessary.

public async Task UpdateDatabase<TEntity>(List<TEntity> newItems)
    where TEntity : IEntityInfo, class
{
    <...>
}

This routine pulls the existing TEntity items from the database, compares them (actually, compares the properties exposed by the IEntityInfo interface) with the newItems list, and adds, modifies, or removes items from the database.

Adding or modifying items is easy. But removing items is problematic. If an existing item (i.e. a tracked entity mapped to a row in the database) has any FK references, deleting the item from the DbContext will fail with a DbUpdateException when UpdateDatabase() is called. At that point, the item is removed (EntityState.Deleted) in the DbContext, but it still exists in the database. And any further calls to UpdateDatabase will fail.

So, I'm looking for a way to determine whether a generic entity can be deleted (i.e. whether the entity has any FK references). (And before someone asks about cascade deletes, the database design is such that all FK references are restricted deletes. In other words, you can't delete a widget if it's on a truck to Omaha, or if some customer has that type of widget in an order.)

The above routine doesn't know anything about the connections between the generic entities that it is given to work with and the rest of the database. It would seem that I have two options:

My preferred option: Ask EF Core if the generic entity has any FK references. I don't think this is possible, but it's worth writing this long post to see if someone has a brilliant suggestion.
Have IEntityInfo include a CanBeDeleted() method. Thus, each entity class can implement its own logic to determine whether or not it can be deleted. The problem with this approach is that it's very fragile. CanBeDeleted() needs to know about every FK in the database that might prevent the item's deletion; this method must be updated any time a new FK reference to the entity is added to the database design.

CodePudding user response：

To determine whether a generic entity has any foreign key (FK) references in Entity Framework Core (EF Core), you can use the HasReferencingForeignKey method on the EntityEntry class. This method takes the name of the navigation property that represents the FK relationship as an argument, and it returns a boolean value indicating whether the entity has any FK references.

Here is an example of how you might use the HasReferencingForeignKey method to determine whether a generic entity has any FK references in EF Core:

public static bool HasReferencingForeignKeys<TEntity>(this DbContext context, TEntity entity)
    where TEntity : class
{
    var entry = context.Entry(entity);

    return entry.Navigations
        .Any(n => entry.HasReferencingForeignKey(n.Metadata.Name));
}

In the code above, we define an extension method that takes a DbContext and an entity as arguments. The method uses the Entry method on the DbContext to get the entity entry for the specified entity, and it uses the Navigations property on the entry to get a list of the navigation properties for the entity.

Next, the method uses the Any method to check if any of the navigation properties have FK references. It does this by calling the HasReferencingForeignKey method on the entity entry for each navigation property, and passing the name of the navigation property as an argument. If any of the navigation properties have FK references, the Any method will return true, indicating that the entity has at least one FK reference.

To use this method, you can call it on a DbContext instance and pass the entity you want to check as an argument. The method will return a boolean value indicating whether the entity has any FK references or not.

Note that this is just one way to determine whether a generic entity has any FK references in EF Core. The specific code and implementation may vary depending on your specific requirements and the entities in your model. You may need to adjust the code above to fit your specific needs.

To determine whether a generic entity can be deleted in Entity Framework Core (EF Core), you can use the CanDelete method on the DeleteBehavior enum. This method takes the current DeleteBehavior value and the IsOwned value for the entity as arguments, and it returns a boolean value indicating whether the entity can be deleted.

Here is an example of how you might use the CanDelete method to determine whether a generic entity can be deleted in EF Core:

public static bool CanDelete<TEntity>(this DbContext context, TEntity entity)
    where TEntity : class
{
    var entry = context.Entry(entity);
    var deleteBehavior = entry.Metadata.GetDeleteBehavior();
    var isOwned = entry.Metadata.IsOwned();

    return DeleteBehavior.CanDelete(deleteBehavior, isOwned);
}

In the code above, we define an extension method that takes a DbContext and an entity as arguments. The method uses the Entry method on the DbContext to get the entity entry for the specified entity, and it uses the Metadata property on the entry to get the metadata for the entity.

Next, the method uses the GetDeleteBehavior and IsOwned methods on the entity metadata to get the DeleteBehavior value and the IsOwned value for the entity, respectively. Finally, the method uses the CanDelete method on the DeleteBehavior enum to determine whether the entity can be deleted based on the current DeleteBehavior value and the IsOwned value.

To use this method, you can call it on a DbContext instance and pass the entity you want to check as an argument. The method will return a boolean value indicating whether the entity can be deleted or not.

Note that this is just one way to determine whether a generic entity can be deleted in EF Core. The specific code and implementation may vary depending on your specific requirements and the entities in your model. You may need to adjust the code above to fit your