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projectFields

@webda/ql

Function: projectFields()

projectFields<T>(object, paths): Partial<T>

Defined in: packages/ql/src/projection.ts:105

Keep only some fields of an object: the projection of a SELECT a, b.c field list

  • b.c keeps { b: { c } }; sibling paths merge (b.c, b.d), and a path listed with one of its parents (b, b.c) keeps the whole parent. Duplicates are ignored.
  • A path through an array applies to each element: tags.name on tags: [{ name, color }] keeps tags: [{ name }].
  • A path through a scalar or null selects nothing: the field is omitted (an array element is dropped). An object on the path is kept, even when none of its fields is selected.
  • A missing value is omitted, an existing null is kept.
  • Keys keep the order of the object, not the order of the paths.
  • A path with a __proto__, constructor or prototype segment is ignored.

The object is not changed. Values selected whole are returned by reference, not copied.

Type Parameters​

T​

T = any

Parameters​

object​

T

the object to project (an array is projected element by element)

paths​

Iterable<string>

dotted field paths to keep

Returns​

Partial<T>

a new object holding the selected fields; a value that is not an object is returned as is