Failing test: UoW unable to break cycles when removing entities without DB-level cascade #10548
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This was referenced Feb 28, 2023
mpdude
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When computing the commit order for entity removals, we have to look out for `@ORM\JoinColumn(onDelete="SET NULL")` to find places where cyclic associations can be broken. #### Background The UoW computes a "commit order" to find the sequence in which tables shall be processed when inserting entities into the database or performing delete operations. For the insert case, the ORM is able to schedule _extra updates_ that will be performed after all entities have been inserted. Associations which are configured as `@ORM\JoinColumn(nullable=true, ...)` can be left as `NULL` in the database when performing the initial `INSERT` statements, and will be updated once all new entities have been written to the database. This can be used to break cyclic associations between entity instances. For removals, the ORM does not currently implement up-front `UPDATE` statements to `NULL` out associations before `DELETE` statements are executed. That means when associations form a cycle, users have to configure `@ORM\JoinColumn(onDelete="SET NULL", ...)` on one of the associations involved. This transfers responsibility to the DBMS to break the cycle at that place. _But_, we still have to perform the delete statements in an order that makes this happen early enough. This may be a _different_ order than the one required for the insert case. We can find it _only_ by looking at the `onDelete` behaviour. We must ignore the `nullable` property, which is irrelevant, since we do not even try to `NULL` anything. #### Example Assume three entity classes `A`, `B`, `C`. There are unidirectional one-to-one associations `A -> B`, `B -> C`, `C -> A`. All those associations are `nullable= true`. Three entities `$a`, `$b`, `$c` are created from these respective classes and associations are set up. All operations `cascade` at the ORM level. So we can test what happens when we start the operations at the three individual entities, but in the end, they will always involve all three of them. _Any_ insert order will work, so the improvements necessary to solve doctrine#10531 or doctrine#10532 are not needed here. Since all associations are between different tables, the current table-level computation is good enough. For the removal case, only the `A -> B` association has `onDelete="SET NULL"`. So, the only possible execution order is `$b`, `$c`, `$a`. We have to find that regardless of where we start the cascade operation. The DBMS will set the `A -> B` association on `$a` to `NULL` when we remove `$b`. We can then remove `$c` since it is no longer being referred to, then `$a`. #### Related cases These cases ask for the ORM to perform the extra update before the delete by itself, without DBMS-level support: * doctrine#5665 * doctrine#10548
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When computing the commit order for entity removals, we have to look out for `@ORM\JoinColumn(onDelete="SET NULL")` to find places where cyclic associations can be broken. #### Background The UoW computes a "commit order" to find the sequence in which tables shall be processed when inserting entities into the database or performing delete operations. For the insert case, the ORM is able to schedule _extra updates_ that will be performed after all entities have been inserted. Associations which are configured as `@ORM\JoinColumn(nullable=true, ...)` can be left as `NULL` in the database when performing the initial `INSERT` statements, and will be updated once all new entities have been written to the database. This can be used to break cyclic associations between entity instances. For removals, the ORM does not currently implement up-front `UPDATE` statements to `NULL` out associations before `DELETE` statements are executed. That means when associations form a cycle, users have to configure `@ORM\JoinColumn(onDelete="SET NULL", ...)` on one of the associations involved. This transfers responsibility to the DBMS to break the cycle at that place. _But_, we still have to perform the delete statements in an order that makes this happen early enough. This may be a _different_ order than the one required for the insert case. We can find it _only_ by looking at the `onDelete` behaviour. We must ignore the `nullable` property, which is irrelevant, since we do not even try to `NULL` anything. #### Example Assume three entity classes `A`, `B`, `C`. There are unidirectional one-to-one associations `A -> B`, `B -> C`, `C -> A`. All those associations are `nullable= true`. Three entities `$a`, `$b`, `$c` are created from these respective classes and associations are set up. All operations `cascade` at the ORM level. So we can test what happens when we start the operations at the three individual entities, but in the end, they will always involve all three of them. _Any_ insert order will work, so the improvements necessary to solve doctrine#10531 or doctrine#10532 are not needed here. Since all associations are between different tables, the current table-level computation is good enough. For the removal case, only the `A -> B` association has `onDelete="SET NULL"`. So, the only possible execution order is `$b`, `$c`, `$a`. We have to find that regardless of where we start the cascade operation. The DBMS will set the `A -> B` association on `$a` to `NULL` when we remove `$b`. We can then remove `$c` since it is no longer being referred to, then `$a`. #### Related cases These cases ask for the ORM to perform the extra update before the delete by itself, without DBMS-level support: * doctrine#5665 * doctrine#10548
mpdude
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When computing the commit order for entity removals, we have to look out for `@ORM\JoinColumn(onDelete="SET NULL")` to find places where cyclic associations can be broken. #### Background The UoW computes a "commit order" to find the sequence in which tables shall be processed when inserting entities into the database or performing delete operations. For the insert case, the ORM is able to schedule _extra updates_ that will be performed after all entities have been inserted. Associations which are configured as `@ORM\JoinColumn(nullable=true, ...)` can be left as `NULL` in the database when performing the initial `INSERT` statements, and will be updated once all new entities have been written to the database. This can be used to break cyclic associations between entity instances. For removals, the ORM does not currently implement up-front `UPDATE` statements to `NULL` out associations before `DELETE` statements are executed. That means when associations form a cycle, users have to configure `@ORM\JoinColumn(onDelete="SET NULL", ...)` on one of the associations involved. This transfers responsibility to the DBMS to break the cycle at that place. _But_, we still have to perform the delete statements in an order that makes this happen early enough. This may be a _different_ order than the one required for the insert case. We can find it _only_ by looking at the `onDelete` behaviour. We must ignore the `nullable` property, which is irrelevant, since we do not even try to `NULL` anything. #### Example Assume three entity classes `A`, `B`, `C`. There are unidirectional one-to-one associations `A -> B`, `B -> C`, `C -> A`. All those associations are `nullable= true`. Three entities `$a`, `$b`, `$c` are created from these respective classes and associations are set up. All operations `cascade` at the ORM level. So we can test what happens when we start the operations at the three individual entities, but in the end, they will always involve all three of them. _Any_ insert order will work, so the improvements necessary to solve doctrine#10531 or doctrine#10532 are not needed here. Since all associations are between different tables, the current table-level computation is good enough. For the removal case, only the `A -> B` association has `onDelete="SET NULL"`. So, the only possible execution order is `$b`, `$c`, `$a`. We have to find that regardless of where we start the cascade operation. The DBMS will set the `A -> B` association on `$a` to `NULL` when we remove `$b`. We can then remove `$c` since it is no longer being referred to, then `$a`. #### Related cases These cases ask for the ORM to perform the extra update before the delete by itself, without DBMS-level support: * doctrine#5665 * doctrine#10548
mpdude
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When computing the commit order for entity removals, we have to look out for `@ORM\JoinColumn(onDelete="SET NULL")` to find places where cyclic associations can be broken. #### Background The UoW computes a "commit order" to find the sequence in which tables shall be processed when inserting entities into the database or performing delete operations. For the insert case, the ORM is able to schedule _extra updates_ that will be performed after all entities have been inserted. Associations which are configured as `@ORM\JoinColumn(nullable=true, ...)` can be left as `NULL` in the database when performing the initial `INSERT` statements, and will be updated once all new entities have been written to the database. This can be used to break cyclic associations between entity instances. For removals, the ORM does not currently implement up-front `UPDATE` statements to `NULL` out associations before `DELETE` statements are executed. That means when associations form a cycle, users have to configure `@ORM\JoinColumn(onDelete="SET NULL", ...)` on one of the associations involved. This transfers responsibility to the DBMS to break the cycle at that place. _But_, we still have to perform the delete statements in an order that makes this happen early enough. This may be a _different_ order than the one required for the insert case. We can find it _only_ by looking at the `onDelete` behaviour. We must ignore the `nullable` property, which is irrelevant, since we do not even try to `NULL` anything. #### Example Assume three entity classes `A`, `B`, `C`. There are unidirectional one-to-one associations `A -> B`, `B -> C`, `C -> A`. All those associations are `nullable= true`. Three entities `$a`, `$b`, `$c` are created from these respective classes and associations are set up. All operations `cascade` at the ORM level. So we can test what happens when we start the operations at the three individual entities, but in the end, they will always involve all three of them. _Any_ insert order will work, so the improvements necessary to solve doctrine#10531 or doctrine#10532 are not needed here. Since all associations are between different tables, the current table-level computation is good enough. For the removal case, only the `A -> B` association has `onDelete="SET NULL"`. So, the only possible execution order is `$b`, `$c`, `$a`. We have to find that regardless of where we start the cascade operation. The DBMS will set the `A -> B` association on `$a` to `NULL` when we remove `$b`. We can then remove `$c` since it is no longer being referred to, then `$a`. #### Related cases These cases ask for the ORM to perform the extra update before the delete by itself, without DBMS-level support: * doctrine#5665 * doctrine#10548
mpdude
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When computing the commit order for entity removals, we have to look out for `@ORM\JoinColumn(onDelete="SET NULL")` to find places where cyclic associations can be broken. #### Background The UoW computes a "commit order" to find the sequence in which tables shall be processed when inserting entities into the database or performing delete operations. For the insert case, the ORM is able to schedule _extra updates_ that will be performed after all entities have been inserted. Associations which are configured as `@ORM\JoinColumn(nullable=true, ...)` can be left as `NULL` in the database when performing the initial `INSERT` statements, and will be updated once all new entities have been written to the database. This can be used to break cyclic associations between entity instances. For removals, the ORM does not currently implement up-front `UPDATE` statements to `NULL` out associations before `DELETE` statements are executed. That means when associations form a cycle, users have to configure `@ORM\JoinColumn(onDelete="SET NULL", ...)` on one of the associations involved. This transfers responsibility to the DBMS to break the cycle at that place. _But_, we still have to perform the delete statements in an order that makes this happen early enough. This may be a _different_ order than the one required for the insert case. We can find it _only_ by looking at the `onDelete` behaviour. We must ignore the `nullable` property, which is irrelevant, since we do not even try to `NULL` anything. #### Example Assume three entity classes `A`, `B`, `C`. There are unidirectional one-to-one associations `A -> B`, `B -> C`, `C -> A`. All those associations are `nullable= true`. Three entities `$a`, `$b`, `$c` are created from these respective classes and associations are set up. All operations `cascade` at the ORM level. So we can test what happens when we start the operations at the three individual entities, but in the end, they will always involve all three of them. _Any_ insert order will work, so the improvements necessary to solve doctrine#10531 or doctrine#10532 are not needed here. Since all associations are between different tables, the current table-level computation is good enough. For the removal case, only the `A -> B` association has `onDelete="SET NULL"`. So, the only possible execution order is `$b`, `$c`, `$a`. We have to find that regardless of where we start the cascade operation. The DBMS will set the `A -> B` association on `$a` to `NULL` when we remove `$b`. We can then remove `$c` since it is no longer being referred to, then `$a`. #### Related cases These cases ask for the ORM to perform the extra update before the delete by itself, without DBMS-level support: * doctrine#5665 * doctrine#10548
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…10566) When computing the commit order for entity removals, we have to look out for `@ORM\JoinColumn(onDelete="SET NULL")` to find places where cyclic associations can be broken. #### Background The UoW computes a "commit order" to find the sequence in which tables shall be processed when inserting entities into the database or performing delete operations. For the insert case, the ORM is able to schedule _extra updates_ that will be performed after all entities have been inserted. Associations which are configured as `@ORM\JoinColumn(nullable=true, ...)` can be left as `NULL` in the database when performing the initial `INSERT` statements, and will be updated once all new entities have been written to the database. This can be used to break cyclic associations between entity instances. For removals, the ORM does not currently implement up-front `UPDATE` statements to `NULL` out associations before `DELETE` statements are executed. That means when associations form a cycle, users have to configure `@ORM\JoinColumn(onDelete="SET NULL", ...)` on one of the associations involved. This transfers responsibility to the DBMS to break the cycle at that place. _But_, we still have to perform the delete statements in an order that makes this happen early enough. This may be a _different_ order than the one required for the insert case. We can find it _only_ by looking at the `onDelete` behaviour. We must ignore the `nullable` property, which is irrelevant, since we do not even try to `NULL` anything. #### Example Assume three entity classes `A`, `B`, `C`. There are unidirectional one-to-one associations `A -> B`, `B -> C`, `C -> A`. All those associations are `nullable= true`. Three entities `$a`, `$b`, `$c` are created from these respective classes and associations are set up. All operations `cascade` at the ORM level. So we can test what happens when we start the operations at the three individual entities, but in the end, they will always involve all three of them. _Any_ insert order will work, so the improvements necessary to solve #10531 or #10532 are not needed here. Since all associations are between different tables, the current table-level computation is good enough. For the removal case, only the `A -> B` association has `onDelete="SET NULL"`. So, the only possible execution order is `$b`, `$c`, `$a`. We have to find that regardless of where we start the cascade operation. The DBMS will set the `A -> B` association on `$a` to `NULL` when we remove `$b`. We can then remove `$c` since it is no longer being referred to, then `$a`. #### Related cases These cases ask for the ORM to perform the extra update before the delete by itself, without DBMS-level support: * #5665 * #10548
…ut DB-level cascade This adds a failing test case for doctrine#5665. In this example, we have a cyclic association between three entities. All associations are NULLable, so the ORM is able to perform the INSERT operation: The cycle can be broken by scheduling an "extra UPDATE" in the UoW. However, the UoW is unable to perform the remove operation. Cyclic references by the foreign keys in the database prevent removal of two of the entities. If the ORM were able to detect this case and perform an UPDATE _before_ the DELETE, the test would pass. As a workaround, `@JoinColumn(onDelete="CASCADE")` can be used. That way, the DBMS will make this UPDATE just in time and without ORM support – but that seems not to be what the OP of doctrine#5665 asked for.
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This adds a failing test case for #5665.
In this example, we have a cyclic association between three entities. All associations are NULLable, so the ORM is able to perform the INSERT operation: The cycle can be broken by scheduling an "extra UPDATE" in the UoW.
However, the UoW is unable to perform the remove operation. Cyclic references by the foreign keys in the database prevent removal of two of the entities.
If the ORM were able to detect this case and perform an UPDATE before the DELETE, the test would pass – this is what the OP of #5665 asks for.
A workaround might be to use
@JoinColumn(onDelete="SET NULL")].