55 lines
2.5 KiB
Plaintext
55 lines
2.5 KiB
Plaintext
created: 20201002010134640
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modified: 20201002012758239
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tags: moduletypes dev
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title: indexer modules
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Indexer modules maintain indexes of tiddlers organized in a manner that's more efficient for different types of access, typically to speed up things like certain filter operators. An example of this would be the tag indexer - it's much faster to maintain a lookup table listing which tiddlers have a given tag than to iterate over //all// of the tiddlers in a wiki and ask each of them if they have the tag you're interested in!
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Indexer modules have a `module-type` of `indexer`, and the indexers that are included with TiddlyWiki can be found under `core/modules/indexers`.
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! Methods
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Indexer modules must export a constructor function, which takes the current wiki object as its only argument. The object built by the construction function must implement the following methods:
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!! `init()`
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This performs any initial setup required by an indexer.
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!! `rebuild()`
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This rebuilds an index from scratch, usually after a large number of changes have happened to a wiki.
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!! `update(updateDescriptor)`
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This is called every time a tiddler is added, changed, or deleted. The `updateDescriptor` value is an object with two fields - `old` and `new` - which represent the pre-update and post-update state of the tiddler, respectively. Each of these has three fields of their own:
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* `tiddler` - the state of the tiddler (may be `null`)
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* `shadow` - a boolean indicating whether or not the tiddler is a shadow
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* `exists` - a boolean indicating whether or not the tiddler exists
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For example, let's say you have an indexer `idx` and you create a tiddler T with the text "test" - that would result in your indexer's `update` method being called like this:
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```javascript
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idx.update({
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old: { tiddler: null, shadow: false, exists: false },
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new: { tiddler: new $tw.Tiddler({title: 'T', text: 'test'}), shadow: false, exists: true }
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});
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```
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If you then change the text from "test" to "testing", `update` would be called like this:
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```javascript
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idx.update({
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old: { tiddler: new $tw.Tiddler({title: 'T', text: 'test'}), shadow: false, exists: true },
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new: { tiddler: new $tw.Tiddler({title: 'T', text: 'testing'}), shadow: false, exists: true }
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});
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```
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And finally, if you delete T, `update` will be called like this:
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```javascript
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idx.update({
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old: { tiddler: new $tw.Tiddler({title: 'T', text: 'testing'}), shadow: false, exists: true },
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new: { tiddler: null, shadow: false, exists: false }
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});
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``` |