Modify to use loader to get index pattern & Add dataSourceRef

[kristenTian]

Description

• Modify to use loader to get index pattern, so UI has the hydrated dataSourceJSON to use.
• populate dataSourceRef in IndexPattern data model

Test

Tested to fetch a index pattern in data source inside visualization:

dataSourceRef: {
id: "1d7fff10-0181-11ed-bf9e-8b2e48184190"
type: "data-source" }

Issues Resolved

TBA

[zhongnansu]

Can you share more about what's blocking you to clean up this field? I mean we don't need to be rush, I can wait for you to complete the clean up and then merge my PR.

[kristenTian]

The dataSourcesJSON is currently used by the UI side as well, so to clean it up, extra work is involved, however, for your side, just rely on dataSourceRef will do the trick. -- I will merge this PR, so we move fast to testing the read from dataSourceRef on visualization side. Just wanna callout that the cleanup is transparent to your side :)

[zhongnansu]

If it's just extracting some info from another field dataSourcesJSON. It can be done anywhere, I can do it from my side too. I wonder is it possible to get rid of the dataSourcesJSON in the data model itself.

[zhongnansu]

I think you are following similar pattern to add xxxJSON to any saved object mapping and interfaces(E.g. see below dashboard.ts). But I didn't see this JSON field being added to the actual index-pattern mapping defined in index_patterns.ts? I am still trying to understand the codebase, so correct me if I am wrong.

OpenSearch-Dashboards/src/plugins/dashboard/server/saved_objects/dashboard.ts

Lines 57 to 65 in e41efcc

	mappings: {
	properties: {
	description: { type: 'text' },
	hits: { type: 'integer', index: false, doc_values: false },
	kibanaSavedObjectMeta: {
	properties: { searchSourceJSON: { type: 'text', index: false } },
	},
	optionsJSON: { type: 'text', index: false },
	panelsJSON: { type: 'text', index: false },

OpenSearch-Dashboards/src/plugins/data/server/saved_objects/index_patterns.ts

Lines 59 to 65 in e41efcc

	mappings: {
	dynamic: false,
	properties: {
	title: { type: 'text' },
	type: { type: 'keyword' },
	},
	},

[kristenTian]

This is a good question, index pattern indeed have lots fields not added to map, e,g, fields, timeFieldName etc. My guess is it's due to they are optional fields.