event-reduce-js
v5.2.7
Published
javascript implementation of the event-reduce algorithm https://pubkey.github.io/event-reduce/
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EventReduce JavaScript Implementation
This is the javascript version of the EventReduce algorithm.
Installation
npm run install event-reduce-js --save
Usage
In the following we will use EventReduce together with minimongo as an example. You can apply the code to any other database.
- First you need some
QueryParams
that can be used by EventReduce to analyze result-event combinations.
import {
getSortFieldsOfQuery,
ChangeEvent,
calculateActionName,
StateResolveFunctionInput,
runAction
} from 'event-reduce-js';
// some stuff must not be coded by hand but is already in the minimongo library
import {
compileDocumentSelector,
compileSort
} from 'minimongo/src/selector';
// create this helper function that can be used for all queries
export function getQueryParamsByMongoQuery(query: MongoQuery): QueryParams<any> {
const sort = query.sort ? query.sort : ['_id'];
return {
// primary key of the documents
primaryKey: '_id',
// a string[] with all fields that are used in the sorting
sortFields: getSortFieldsOfQuery(query),
skip: query.skip ? query.skip : undefined,
limit: query.limit ? query.limit : undefined,
// a function that returns true if the given document matches the query's selector
queryMatcher: compileDocumentSelector(query.selector),
// a function that can be used as comparator in Array.sort() (returns 1 or -1)
sortComparator: compileSort(sort)
};
}
const exampleQuery: MongoQuery = {
selector: {
age: {
$gt: 18
},
gender: 'm'
},
limit: 10,
sort: ['name', '_id']
};
const queryParams = getQueryParamsByMongoQuery(exampleQuery);
- Now lets say you have an
changeEvent
from whatever changestream or observable your database provides. You also have thecurrentResults
of the query.
// build the input
const input: StateResolveFunctionInput<DocumentType> = {
// the changeEvent
changeEvent,
// queryParams from above
queryParams,
// array with previous results documents
previousResults: currentResults,
// key->document map with previous results indexed by primary key
// (optional) improves performance
keyDocumentMap: currentDocMap
};
// calculate the correct action name
const action = calculateActionName(input);
if (action === 'runFullQueryAgain') {
/**
* when EventReduce could not optimize the input,
* we get the actionName 'runFullQueryAgain'
* and run the query over the database again
*/
currentResults = await implementation.getRawResults(query);
// also refresh the key-document map
currentDocMap.clear();
currentResults.forEach(doc => currentDocMap.set(doc._id, doc));
} else {
// event-reduce could optimize the event, run the action function
runAction(
action,
queryParams,
changeEvent,
currentResults,
currentDocMap
);
}
// show new results
// notice that for performance resons,
// the functions of event-reduce will mutate the input variables
console.dir(currentResults);