Terraform updates on Discovery Engine data store ids causes an unexpected delete and recreated

[khuong507]

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The discovery engine api supports the ability to patch an engine. By patching it should allow terraform to be able to update the
google_discovery_engine_chat_engine resource rather than deleting and replacing. Today when adding a new datastore to the data_store_ids collection it forces a delete an recreate. This is unappealing. Especially if the engine has been heavily tuned with custom tuned models. Deleting and recreating causes a lot of unnecessary work. The GCP UI supports adding/removing data stores without having to delete the app. The Terraform resource should do the same.

https://cloud.google.com/generative-ai-app-builder/docs/reference/rest/v1/projects.locations.collections.engines/patch

Terraform Version & Provider Version(s)

Terraform v1.5.7
on darwin_arm64

• provider registry.terraform.io/hashicorp/archive v2.6.0
• provider registry.terraform.io/hashicorp/google v6.12.0
• provider registry.terraform.io/hashicorp/google-beta v5.7.0

Affected Resource(s)

google_discovery_engine_chat_engine

Terraform Configuration

resource "google_discovery_engine_chat_engine" "primary" {
  engine_id = "chat-engine-id"
  collection_id = "default_collection"
  location = google_discovery_engine_data_store.test_data_store.location
  display_name = "Chat engine"
  industry_vertical = "GENERIC"
  data_store_ids = [google_discovery_engine_data_store.test_data_store.data_store_id, google_discovery_engine_data_store.test_data_store_2.data_store_id]
  common_config {
    company_name = "test-company"
  }
  chat_engine_config {
    agent_creation_config {
    business = "test business name"
    default_language_code = "en"
    time_zone = "America/Los_Angeles"
    }
  }
}

Debug Output

-/+ resource "google_discovery_engine_search_engine" "hidden" {
      + create_time       = (known after apply)
      ~ data_store_ids    = [ # forces replacement
          - "store1",
          + "store1",
            "store2",
            # (3 unchanged elements hidden)
        ]
      ~ id                = "hidden" -> (known after apply)
      ~ name              = "hidden" -> (known after apply)
      + update_time       = (known after apply)
        # (6 unchanged attributes hidden)

        # (2 unchanged blocks hidden)
    }

Expected Behavior

The google_discovery_engine_search_engine should be modified/updated and not deleted and recreated.

Actual Behavior

The google_discovery_engine_search_engine resource is deleted and recreated.

Steps to reproduce

1. With the following configs create an engine:

resource "google_discovery_engine_chat_engine" "primary" {
  engine_id = "chat-engine-id"
  collection_id = "default_collection"
  location = google_discovery_engine_data_store.test_data_store.location
  display_name = "Chat engine"
  industry_vertical = "GENERIC"
  data_store_ids = [google_discovery_engine_data_store.test_data_store.data_store_id, google_discovery_engine_data_store.test_data_store_2.data_store_id]
  common_config {
    company_name = "test-company"
  }
  chat_engine_config {
    agent_creation_config {
    business = "test business name"
    default_language_code = "en"
    time_zone = "America/Los_Angeles"
    }
  }
}

2. terraform apply
3. Modify the data store ids by removing one:

resource "google_discovery_engine_chat_engine" "primary" {
  engine_id = "chat-engine-id"
  collection_id = "default_collection"
  location = google_discovery_engine_data_store.test_data_store.location
  display_name = "Chat engine"
  industry_vertical = "GENERIC"
  data_store_ids = [google_discovery_engine_data_store.test_data_store.data_store_id]
  common_config {
    company_name = "test-company"
  }
  chat_engine_config {
    agent_creation_config {
    business = "test business name"
    default_language_code = "en"
    time_zone = "America/Los_Angeles"
    }
  }
}

4. terraform apply

Important Factoids

No response

References

No response

b/382548791