Feat!: Add support for virtual statements to be executed post update

[themisvaltinos]

This update introduces statements that are executed after a virtual update. These can be used for example to grant privileges on views of the virtual layer.

These expressions should be defined within a ON_VIRTUAL_UPDATE_BEGIN; ...; ON_VIRTUAL_UPDATE_END; block. For example:

MODEL (
  name db.customers 
);

SELECT 
  item_id
FROM 
  db.seed_model;

ON_VIRTUAL_UPDATE_BEGIN; 

GRANT SELECT ON VIEW @this_model TO ROLE role_name;

INJA_STATEMENT_BEGIN;     
GRANT REFERENCES, SELECT ON FUTURE VIEWS IN DATABASE {{ db }} TO ROLE owner_name;  
JINJA_END;  

ON_VIRTUAL_UPDATE_END;

Jinja expressions are also supported within this block by properly nesting the Jinja block as shown in the example above.

In these statements table resolution occurs at the virtual level, meaning that qualified view names (including @this_model) are used instead of the physical table names. For example, when running the plan in an environment named dev, the db.customers as well as this_model would resolve to db__dev.customers rather than the physical table.

For python models these statements are defined in the @model decorator:

@model( 
  "db.customers",  
  on_virtual_update=["GRANT SELECT ON VIEW @this_model TO ROLE role_name;"]
)

[georgesittas]

Should we add an end-to-end test for this?

[georgesittas]

I wonder if we wanna make a helper for this, there are a few places where we do the same thing in the codebase:

• sqlmesh/sqlmesh/core/snapshot/evaluator.py

  Lines 722 to 725 in 2adf5a1

  	parent_snapshots_by_name = {
  	snapshots[p_sid].name: snapshots[p_sid] for p_sid in snapshot.parents
  	}
  	parent_snapshots_by_name[snapshot.name] = snapshot

• sqlmesh/sqlmesh/core/snapshot/evaluator.py

  Lines 821 to 824 in 2adf5a1

  	parent_snapshots_by_name = {
  	snapshots[p_sid].name: snapshots[p_sid] for p_sid in snapshot.parents
  	}
  	parent_snapshots_by_name[snapshot.name] = snapshot

• sqlmesh/sqlmesh/core/scheduler.py

  Lines 164 to 167 in 2adf5a1

  	snapshots = {
  	self.snapshots[p_sid].name: self.snapshots[p_sid] for p_sid in snapshot.parents
  	}
  	snapshots[snapshot.name] = snapshot

cc @izeigerman

[izeigerman]

oh yeah, good catch lol. Yeah, we can add one in the snapshot/definition.py

[izeigerman]

Can we please make sure this feature is documented before we merge.