Implement deferrable foreign keys for SAP HANA

[alumni]

Related feature request: #6098, #2191.

I've added deferrable (check time) options for foreign keys on SAP HANA. See <references_specification> in the CREATE TABLE and ALTER TABLE specification:

<references_specification> ::= 
  REFERENCES <referenced_table> [ ( <referenced_column_name_list> ) ]
  [ <referential_triggered_action> ]
  [ <constraint_enforcement> ]
  [ <constraint_check_time> ]
<constraint_check_time> ::= INITIALLY { IMMEDIATE | DEFERRED }

as well as the REFERENTIAL_CONSTRAINTS system table in their official documentation:

Column name	Data type	Description
CHECK_TIME	STRING	The time when the constraint is checked: INITIALLY_IMMEDIATE or INITIALLY DEFERRED.

Notes:

• The implementation is using the already defined deferrable attribute in RelationOptions, that has the possible values INITIALLY IMMEDIATE and INITIALLY DEFERRED, same as the specification for the REFERENCES SQL expression.
• In the REFERENTIAL_CONSTRAINTS table, the possible values are INITIALLY_IMMEDIATE (with underscore) and INITIALLY DEFERRED (with space).

[imnotjames]

You need to add tests for this feature.

[pleerock]

Looks like no response from author, closing it.

[alumni]

There was nothing to respond, tests for HANA are non-existent and the local test setup is not described anywhere as far as I remember.

[alumni]

BTW, we maintain a lot of patches for the HANA driver locally, we just avoid creating PRs for this reason. We test them as part of our E2E, but since we have no idea how to run the TypeORM tests with HANA locally + the slow PR review process makes us avoid submitting PRs.

[pleerock]

It can be a good contribution if you find the way to setup SAP Hana on CI.

Then it will simplify process of merging (at least we can be sure nothing was broke).
Also it will simplify your experience when you upgrade ORM version.

[alumni]

@pleerock The easiest way would be with a HANA Cloud instance. The only required setup in that case would be the hostname and the credentials. Then every time the tests are run a DB schema could be created for that run and dropped when it's over. The main question would be how to get access to a HANA Cloud instance (it could get quite pricey) - maybe SAP could donate it?

[pleerock]

We need something free. Can't we simply setup something in a docker container for our CI?

[alumni]

@pleerock HANA Cloud (v4.0) has a free trial (I think it's limited to 30 days but can be extended to 90 days). Not sure how to get the free 1 year advertised on their website.

There's also the possibility to run HANA express (v2.0) inside a container, it seems it's free up to 32gb memory:

• https://developers.sap.com/tutorials/hxe-ua-install-using-docker.html
• https://hub.docker.com/_/sap-hana-express-edition

[pleerock]

HANA Cloud (v4.0) has a free trial (I think it's limited to 30 days but can be extended to 90 days). Not sure how to get the free 1 year advertised on their website.

if it has a time period limit its not an option for us.

There's also the possibility to run HANA express (v2.0) inside a container, it seems it's free up to 32gb memory:

would be great if someone can contribute and setup sap-hana-express-edition container in our CI, so we can run tests inside it.

[AlexMesser]

thank you for contribution!