stream-schema-detector

Detect schema of event streams.

detectSchema(object)

Can detect the schema of a single object:

const { detectSchema } = require('./main');

const schema = detectSchema({ a: 23, b: { c: true, d: [12, true] } });

// schema is:
{
  'a': ['number'],
  'b': ['object'],
  'b.c': ['boolean'],
  'b.d': ['array'],
  'b.d[]': ['number']
}

createStreamSchemaDetector({ loadSchema, saveSchema, maxCacheSize })

Creates a detect function which will detect the schema of multiple events by type and update them when detected schema differs from stored version.

• loadSchema(typeParam):

  called when no cached schema is found for given typeParam, should return a saved schema. typeParam could be any json strigifiable value.

• saveSchema(typeParam, schema, exampleItem):

  called when the detected schema differs from one returned by loadSchema.

• maxCacheSize

  the number of schemas to cache in memory (default is 500)

• detect(typeParam, item):

  the returned function, can be called with a typeParam and an item we want to inspect.

  Will call loadSchema for the given typeParam and compare its return value with the detected schema of the item. Calls saveSchema if detected schema differs from saved one.

  The result of loadSchema is cached in memory, it will only be called once for each typeParam until no differences are detected.

const { createStreamSchemaDetector } = require('./main');

const schemaStore = {};
const loadSchema = async typeId => schemaStore[typeId];
const saveSchema = async (typeId, schema) => {
  schemaStore[typeId] = schema;
};

const detect = createStreamSchemaDetector({ loadSchema, saveSchema });

await detect('browse_events', { a: 4, b: 'hat' });
await detect('browse_events', { a: 23, b: true, c: 14 });
await detect('purchase', { x: 2 });

// content of schemaStore:
{
  'browse_events': { a: ['number'], b: ['string', 'boolean'], c: ['number'] },
  'purchase': { x: ['number'] }
}

Using object as typeParam

const schemaStore = {};
const loadSchema = async ({ source, type }) => schemaStore[`${source}_${type}`];
const saveSchema = async ({ source, type }, schema) => {
  schemaStore[`${source}_${type}`] = schema;
};

const detect = createStreamSchemaDetector({ loadSchema, saveSchema });

await detect({ source: 'A', type: 'x' }, { a: 4});

// schemaStore:
{ 'A_x': { a: ['number'] } }