Entity Framework Remove vs DeleteObject

Question

You can remove an item from a database using EF by using the following two methods    EntityCollection Remove Method ObjectContext DeleteObject Method   The first is on the EntityCollection and the second on the ObjectContext   When should each be used    Is one prefered over the other   Remove   returns a bool and DeleteObject   returns void

User · Answer

If you really want to use Deleted  you d have to make your foreign keys nullable  but then you d end up with orphaned records  which is one of the main reasons you shouldn t be doing that in the first place   So just use Remove    ObjectContext DeleteObject entity  marks the entity as Deleted in the context   It s EntityState is Deleted after that   If you call SaveChanges afterwards EF sends a SQL DELETE statement to the database  If no referential constraints in the database are violated the entity will be deleted  otherwise an exception is thrown   EntityCollection Remove childEntity  marks the relationship between parent and childEntity as Deleted  If the childEntity itself is deleted from the database and what exactly happens when you call SaveChanges depends on the kind of relationship between the two   A thing worth noting is that setting  State   EntityState Deleted does not trigger automatically detected change   archive

User · Answer

It s not generally correct that you can  remove an item from a database  with both methods  To be precise it is like so    ObjectContext DeleteObject entity  marks the entity as Deleted in the context   It s EntityState is Deleted after that   If you call SaveChanges afterwards EF sends a SQL DELETE statement to the database  If no referential constraints in the database are violated the entity will be deleted  otherwise an exception is thrown  EntityCollection Remove childEntity  marks the relationship between parent and childEntity as Deleted  If the childEntity itself is deleted from the database and what exactly happens when you call SaveChanges depends on the kind of relationship between the two    If the relationship is optional  i e  the foreign key that refers from the child to the parent in the database allows NULL values  this foreign will be set to null and if you call SaveChanges this NULL value for the childEntity will be written to the database  i e  the relationship between the two is removed   This happens with a SQL UPDATE statement  No DELETE statement occurs  If the relationship is required  the FK doesn t allow NULL values  and the relationship is not identifying  which means that the foreign key is not part of the child s  composite  primary key  you have to either add the child to another parent or you have to explicitly delete the child  with DeleteObject then   If you don t do any of these a referential constraint is violated and EF will throw an exception when you call SaveChanges - the infamous  The relationship could not be changed because one or more of the foreign-key properties is non-nullable  exception or similar  If the relationship is identifying  it s necessarily required then because any part of the primary key cannot be NULL  EF will mark the childEntity as Deleted as well  If you call SaveChanges a SQL DELETE statement will be sent to the database  If no other referential constraints in the database are violated the entity will be deleted  otherwise an exception is thrown     I am actually a bit confused about the Remarks section on the MSDN page you have linked because it says   If the relationship has a referential integrity constraint  calling the Remove method on a dependent object marks both the relationship and the dependent object for deletion    This seems unprecise or even wrong to me because all three cases above have a  referential integrity constraint  but only in the last case the child is in fact deleted   Unless they mean with  dependent object  an object that participates in an identifying relationship which would be an unusual terminology though

[c#] Entity Framework .Remove() vs. .DeleteObject()

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