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docs/developer/architecture/development-plugin-saved-objects.asciidoc
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[[development-plugin-saved-objects]] | ||
== Using Saved Objects | ||
|
||
Saved Objects allow {kib} plugins to use {es} like a primary | ||
database. Think of it as an Object Document Mapper for {es}. Once a | ||
plugin has registered one or more Saved Object types, the Saved Objects client | ||
can be used to query or perform create, read, update and delete operations on | ||
each type. | ||
|
||
By using Saved Objects your plugin can take advantage of the following | ||
features: | ||
|
||
* Migrations can evolve your document's schema by transforming documents and | ||
ensuring that the field mappings on the index are always up to date. | ||
* a <<saved-objects-api,HTTP API>> is automatically exposed for each type (unless | ||
`hidden=true` is specified). | ||
* a Saved Objects client that can be used from both the server and the browser. | ||
* Users can import or export Saved Objects using the Saved Objects management | ||
UI or the Saved Objects import/export API. | ||
* By declaring `references`, an object's entire reference graph will be | ||
exported. This makes it easy for users to export e.g. a `dashboard` object and | ||
have all the `visualization` objects required to display the dashboard | ||
included in the export. | ||
* When the X-Pack security and spaces plugins are enabled these transparently | ||
provide RBAC access control and the ability to organize Saved Objects into | ||
spaces. | ||
|
||
This document contains developer guidelines and best-practices for plugins | ||
wanting to use Saved Objects. | ||
|
||
=== Registering a Saved Object type | ||
Saved object type definitions should be defined in their own `my_plugin/server/saved_objects` directory. | ||
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The folder should contain a file per type, named after the snake_case name of the type, and an `index.ts` file exporting all the types. | ||
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.src/plugins/my_plugin/server/saved_objects/dashboard_visualization.ts | ||
[source,typescript] | ||
---- | ||
import { SavedObjectsType } from 'src/core/server'; | ||
export const dashboardVisualization: SavedObjectsType = { | ||
name: 'dashboard_visualization', // <1> | ||
hidden: false, | ||
namespaceType: 'single', | ||
mappings: { | ||
dynamic: false, | ||
properties: { | ||
description: { | ||
type: 'text', | ||
}, | ||
hits: { | ||
type: 'integer', | ||
}, | ||
}, | ||
}, | ||
migrations: { | ||
'1.0.0': migratedashboardVisualizationToV1, | ||
'2.0.0': migratedashboardVisualizationToV2, | ||
}, | ||
}; | ||
---- | ||
<1> Since the name of a Saved Object type forms part of the url path for the | ||
public Saved Objects HTTP API, these should follow our API URL path convention | ||
and always be written as snake case. | ||
|
||
.src/plugins/my_plugin/server/saved_objects/index.ts | ||
[source,typescript] | ||
---- | ||
export { dashboardVisualization } from './dashboard_visualization'; | ||
export { dashboard } from './dashboard'; | ||
---- | ||
|
||
.src/plugins/my_plugin/server/plugin.ts | ||
[source,typescript] | ||
---- | ||
import { dashboard, dashboardVisualization } from './saved_objects'; | ||
export class MyPlugin implements Plugin { | ||
setup({ savedObjects }) { | ||
savedObjects.registerType(dashboard); | ||
savedObjects.registerType(dashboardVisualization); | ||
} | ||
} | ||
---- | ||
|
||
=== Mappings | ||
Each Saved Object type can define it's own {es} field mappings. | ||
Because multiple Saved Object types can share the same index, mappings defined | ||
by a type will be nested under a top-level field that matches the type name. | ||
|
||
For example, the mappings defined by the `dashboard_visualization` Saved | ||
Object type: | ||
|
||
.src/plugins/my_plugin/server/saved_objects/dashboard_visualization.ts | ||
[source,typescript] | ||
---- | ||
import { SavedObjectsType } from 'src/core/server'; | ||
export const dashboardVisualization: SavedObjectsType = { | ||
name: 'dashboard_visualization', | ||
... | ||
mappings: { | ||
properties: { | ||
dynamic: false, | ||
description: { | ||
type: 'text', | ||
}, | ||
hits: { | ||
type: 'integer', | ||
}, | ||
}, | ||
}, | ||
migrations: { ... }, | ||
}; | ||
---- | ||
|
||
Will result in the following mappings being applied to the `.kibana` index: | ||
[source,json] | ||
---- | ||
{ | ||
"mappings": { | ||
"dynamic": "strict", | ||
"properties": { | ||
... | ||
"dashboard_vizualization": { | ||
"dynamic": false, | ||
"properties": { | ||
"description": { | ||
"type": "text", | ||
}, | ||
"hits": { | ||
"type": "integer", | ||
}, | ||
}, | ||
} | ||
} | ||
} | ||
} | ||
---- | ||
|
||
Do not use field mappings like you would use data types for the columns of a | ||
SQL database. Instead, field mappings are analogous to a SQL index. Only | ||
specify field mappings for the fields you wish to search on or query. By | ||
specifying `dynamic: false` in any level of your mappings, {es} will | ||
accept and store any other fields even if they are not specified in your mappings. | ||
|
||
Since {es} has a default limit of 1000 fields per index, plugins | ||
should carefully consider the fields they add to the mappings. Similarly, | ||
Saved Object types should never use `dynamic: true` as this can cause an | ||
arbitrary amount of fields to be added to the `.kibana` index. | ||
|
||
=== References | ||
When a Saved Object declares `references` to other Saved Objects, the | ||
Saved Objects Export API will automatically export the target object with all | ||
of it's references. This makes it easy for users to export the entire | ||
reference graph of an object. | ||
|
||
If a Saved Object can't be used on it's own, that is, it needs other objects | ||
to exist for a feature to function correctly, that Saved Object should declare | ||
references to all the objects it requires. For example, a `dashboard` | ||
object might have panels for several `visualization` objects. When these | ||
`visualization` objects don't exist, the dashboard cannot be rendered | ||
correctly. The `dashboard` object should declare references to all it's | ||
visualizations. | ||
|
||
However, `visualization` objects can continue to be rendered or embedded into | ||
other dashboards even if the `dashboard` it was originally embedded into | ||
doesn't exist. As a result, `visualization` objects should not declare | ||
references to `dashboard` objects. | ||
|
||
For each referenced object, an `id`, `type` and `name` are added to the | ||
`references` array: | ||
|
||
[source, typescript] | ||
---- | ||
router.get( | ||
{ path: '/some-path', validate: false }, | ||
async (context, req, res) => { | ||
const object = await context.core.savedObjects.client.create( | ||
'dashboard', | ||
{ | ||
title: 'my dashboard', | ||
panels: [ | ||
{ visualization: 'vis1' }, // <1> | ||
], | ||
indexPattern: 'indexPattern1' | ||
}, | ||
{ references: [ | ||
{ id: '...', type: 'visualization', name: 'vis1' }, | ||
{ id: '...', type: 'index_pattern', name: 'indexPattern1' }, | ||
] | ||
} | ||
) | ||
... | ||
} | ||
); | ||
---- | ||
<1> Note how `dashboard.panels[0].visualization` stores the `name` property of | ||
the reference (not the `id` directly) to be able to uniquely identify this | ||
reference. This guarantees that the id the reference points to always remains | ||
up to date. If a visualization `id` was directly stored in | ||
`dashboard.panels[0].visualization` there is a risk that this `id` gets | ||
updated without updating the reference in the references array. | ||
|
||
==== Writing Migrations | ||
|
||
Saved Objects support schema changes between Kibana versions, which we call | ||
migrations. Migrations are applied when a Kibana installation is upgraded from | ||
one version to the next, when exports are imported via the Saved Objects | ||
Management UI, or when a new object is created via the HTTP API. | ||
|
||
Each Saved Object type may define migrations for its schema. Migrations are | ||
specified by the Kibana version number, receive an input document, and must | ||
return the fully migrated document to be persisted to Elasticsearch. | ||
|
||
Let's say we want to define two migrations: | ||
- In version 1.1.0, we want to drop the `subtitle` field and append it to the | ||
title | ||
- In version 1.4.0, we want to add a new `id` field to every panel with a newly | ||
generated UUID. | ||
|
||
First, the current `mappings` should always reflect the latest or "target" | ||
schema. Next, we should define a migration function for each step in the schema | ||
evolution: | ||
|
||
src/plugins/my_plugin/server/saved_objects/dashboard_visualization.ts | ||
[source,typescript] | ||
---- | ||
import { SavedObjectsType, SavedObjectMigrationFn } from 'src/core/server'; | ||
import uuid from 'uuid'; | ||
interface DashboardVisualizationPre110 { | ||
title: string; | ||
subtitle: string; | ||
panels: Array<{}>; | ||
} | ||
interface DashboardVisualization110 { | ||
title: string; | ||
panels: Array<{}>; | ||
} | ||
interface DashboardVisualization140 { | ||
title: string; | ||
panels: Array<{ id: string }>; | ||
} | ||
const migrateDashboardVisualization110: SavedObjectMigrationFn< | ||
DashboardVisualizationPre110, // <1> | ||
DashboardVisualization110 | ||
> = (doc) => { | ||
const { subtitle, ...attributesWithoutSubtitle } = doc.attributes; | ||
return { | ||
...doc, // <2> | ||
attributes: { | ||
...attributesWithoutSubtitle, | ||
title: `${doc.attributes.title} - ${doc.attributes.subtitle}`, | ||
}, | ||
}; | ||
}; | ||
const migrateDashboardVisualization140: SavedObjectMigrationFn< | ||
DashboardVisualization110, | ||
DashboardVisualization140 | ||
> = (doc) => { | ||
const outPanels = doc.attributes.panels?.map((panel) => { | ||
return { ...panel, id: uuid.v4() }; | ||
}); | ||
return { | ||
...doc, | ||
attributes: { | ||
...doc.attributes, | ||
panels: outPanels, | ||
}, | ||
}; | ||
}; | ||
export const dashboardVisualization: SavedObjectsType = { | ||
name: 'dashboard_visualization', // <1> | ||
/** ... */ | ||
migrations: { | ||
// Takes a pre 1.1.0 doc, and converts it to 1.1.0 | ||
'1.1.0': migrateDashboardVisualization110, | ||
// Takes a 1.1.0 doc, and converts it to 1.4.0 | ||
'1.4.0': migrateDashboardVisualization140, // <3> | ||
}, | ||
}; | ||
---- | ||
<1> It is useful to define an interface for each version of the schema. This | ||
allows TypeScript to ensure that you are properly handling the input and output | ||
types correctly as the schema evolves. | ||
<2> Returning a shallow copy is necessary to avoid type errors when using | ||
different types for the input and output shape. | ||
<3> Migrations do not have to be defined for every version. The version number | ||
of a migration must always be the earliest Kibana version in which this | ||
migration was released. So if you are creating a migration which will be | ||
part of the v7.10.0 release, but will also be backported and released as | ||
v7.9.3, the migration version should be: 7.9.3. | ||
|
||
Migrations should be written defensively, an exception in a migration function | ||
will prevent a Kibana upgrade from succeeding and will cause downtime for our | ||
users. Having said that, if a document is encountered that is not in the | ||
expected shape, migrations are encouraged to throw an exception to abort the | ||
upgrade. In most scenarios, it is better to fail an upgrade than to silently | ||
ignore a corrupt document which can cause unexpected behaviour at some future | ||
point in time. | ||
|
||
It is critical that you have extensive tests to ensure that migrations behave | ||
as expected with all possible input documents. Given how simple it is to test | ||
all the branch conditions in a migration function and the high impact of a bug | ||
in this code, there's really no reason not to aim for 100% test code coverage. |
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