mongo-helpers

A package that provides some test and production helpers

Production

unionOfProjections - takes an array of projections and combines them into a single projection, handling nested and flat projections (but not a mix) as well as array operators.

unionOfProjections([
  { a: 1},
  { a:
    { b: 1}
  }
]) // { a: 1 }


unionOfProjections([
  { a: 1},
  { a: { $elemMatch: 1} }
]) // { a: 1 }

unionOfProjections([
  { a: 1},
  { b: 1 }
]) // { a: 1, b: 1 }

unionOfProjections([
  { a: 1 },
  { b: 0 }
]) // { b: 0 }

We also expose the types

• NestedProjectionOfTSchema which allows the defininition of a projection for a complex mongo schema - including array operations.
• WithCursorDescription - indicating a cursor exposes a valid cursorDescription
• CursorDescription - which defines a filter + options (skip, limit, projection, sort)

Test helpers

We expose FakeCollection and FakeFindCursor. These are very lightweight partial implementations of the mongo API in memory, not suitable for production but generally acceptable for testing.

These have peer dependencies:

• @blastjs/minimongo

Types

exposes ProjectionOfTSchema and FilterOfTSchema which provide strict typechecking on the projection and filter of a schema. Can be used as follows:

  type TSchema = { a: { b: number, c: string }, d: { e: number, f: string }[]}
  const filter: FilterOfTSchema<TSchema> = {
    "a.b": { $gt: 1 },
    "a.c": /whatever/
    "d.e": { $lt: 1 },
    "d.f": /whatever/,
    "d.0.f": /whatever/,
    d: { $elemMatch: { e: { $gt: 1 } }}
  }

The filter item will be strictly checked such that you don't make common mistakes like:

  const filter: FilterOfTSchema<TSchema> = {
    a: {
      b: 1
    }// invalid because it's looking for an element of `a` which is literally b: 1 vs any `a` with b: 1, or a complete and valid `a`
  }

Simiarly, the ProjectionOfTSchema can be used as follows:

  const projection: ProjectionOfTSchema<TSchema> = {
    a: {
      b: 1
    },
    "a.c": 1,
    d: { $slice: -1 },
  }