feat: batchedQuery

[lxsmnsyc]

Adds batchedQuery. It collects calls made at the same time and answers them with one read. This helps when many components each fetch one item as they mount, like rows in a list.

Usage

const getUser = query(
  batchedQuery(
    async (ids: string[]) => {
      const users = await fetchUsers(ids);
      return new Map(users.map(user => [user.id, user]));
    },
    (users, id) => users.get(id)
  ),
  "user"
);

Changes

• batchedQuery(callback, lookup, options?) returns a function that takes one query and resolves with its result.
• callback gets every query collected in one tick and reads them together.
• lookup picks each caller's result from the data. It also gets the query's position in the list.
• Repeated queries are sent to callback once. By default they match by hashKey, the same function query uses for its keys. Pass key to match them another way.
• limit caps how many queries one callback call gets. Extra queries go to more calls. This is useful when ids go into a URL.
• wait sets how long calls are collected, in milliseconds. The default is 0.
• A failed callback rejects only the callers in that call. A lookup that throws rejects only the callers of that query.
• A call made while callback is running starts a new batch. It never gets data from a batch it was not part of.
• On the server, each call runs on its own. The queue is shared by the whole module, so batching there would mix queries from separate requests and run them with the first request's context.
• batchedQuery and the BatchOptions type are exported from the package.

Testing

• Added test/data/batched-query.spec.ts with tests for batching, repeated queries, limit, failed reads, failed lookups, calls made after or during a read, and custom keys.

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Latest commit: 2f56dd4

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