Add implementation for clearing cache table

[hjk1030]

Added a function to delete all the data in the cache table. Trying to resolve issue #122.

[hjk1030]

By the way, do I need to add tests for this?

[ttt-77]

By the way, do I need to add tests for this?

Yes.

[hjk1030]

I modified an existing test to validate this since adding another test makes the existing test fail.

[hjk1030]

I modified the code style. Also changes the delete order to depend on foreign key references.

[hjk1030]

@ttt-77 Could you please review this PR again?

[ttt-77]

Looks good to me. @ddkang

[hjk1030]

@ddkang Could you please review this?

[hjk1030]

I refactored the function using the topological order of inference services.

[ddkang]

@ttt-77 please check

[hjk1030]

@ttt-77 Could you please review this?

[hjk1030]

I've reconsidered the clearing logic. Now I'm planning to use the following procedure:

1. Collect the output tables directly related to the selected services.
2. Collect the output tables that need to be cleared considering the fk constraints and service constraints (if one of the output tables in a service needs to be cleared, all the tables belonging to the service have to be cleared as well). This will use the table_graph in the config, and I'll create a new map at the beginning to get all the services related to a table(I didn't find an existing map for this).
3. Delete the cache tables. No fk refers to the cache table so this should not cause a problem.
4. Delete the output tables in the reversed topological order of table_graph.

Are there any problems with this procedure? Or can it be simplified in some way?

[ttt-77]

Looks good.

[hjk1030]

@ttt-77 Could you please check this? The clearing steps are more complicated than I thought but I think all the steps are necessary.