$$lookup

Joins multiple arrays of objects by a dynamic condition (transformer) on each pair of matches

Usage

{
  "$$lookup": [ /* values */ ],
  "using": [
    { "with": [ /* values 2 */], "as": /* name 2 */, "on": /* Transformer */ },
    { "with": [ /* values 3 */], "as": /* name 3 */, "on": /* Transformer */ },
    ...
  ],
  "to": /* Transformer */
}

Returns

array (of type of to's result or the merge of both primary array's item and with's item)

Arguments

Argument	Type	Values	Required / Default Value	Description
Primary	array	Array of objects	Yes	Array of elements
using	array	Array of UsingEntrys	Yes	Array of defitinitions of how to match other arrays to the main one
to	Transformer(##current,##{as-1},...)	Input is ##current (current element) & ##{as-1} (matched element from with)	Merge ##current with ##match (Append & Overwrite)	Transformer to map each pair of elements to its value in the result array

UsingEntity

Argument	Type	Values	Required / Default Value	Description
with	array	Array of objects	Yes	Array of elements to match with
as	string		Yes	The name the elements from this entry will be referred as
on	Transformer(##current,##index,##{as})	Input is ##current (current element), ##index (current index) & ##{as} the matched element from the array (replace {as} with the name provided in as argument)	Yes	Evaluated condition on when to match an element from the main array and with array (uses the Truthy logic)

Examples

Input

Definition

Output

{
  "a": [
    { "id": 2, "a": 1 },
    { "id": 5, "a": 2 }
  ],
  "b":[
    { "id": 2, "a": "x" },
    { "id": 5, "e": true }
  ]
}

{
  "$$lookup": "$.a",
  "using": [
    {
      "with": "$.b",
      "as": "match",
      "on": {
        "$$is": "##current.id",
        "eq": "##match.id"
      }
    }
  ]
}

[
  { 
    "id": 2, 
    "a": "x"
  },
  { 
    "id": 5, 
    "a": 2, 
    "e": true
  }
]

{
  "a": [
    { "id": 2, "a": 1 },
    { "id": 5, "a": 2 }
  ],
  "b":[
    { "key": 2, "a": "x" },
    { "key": 5, "e": true }
  ]
}

{
  "$$lookup": "$.a",
  "using": [
    {
      "with": "$.b",
      "as": "match",
      "on": {
        "$$is": "##current.id",
        "eq": "##match.key"
      }
    }
  ]
}

[
  { 
    "id": 2, 
    "a": "x", 
    "key": 2
  },
  { 
    "id": 5, 
    "a": 2, 
    "e": true, 
    "key": 5
  }
]

{
  "a": [
    { "id": 2, "a": 1 },
    { "id": 5, "a": 2 }
  ],
  "b":[
    { "id": 2, "a": "x" },
    { "id": 5, "e": true }
  ]
}

{
  "$$lookup": "$.a",
  "using": [
    {
      "with": "$.b",
      "as": "match",
      "on": {
        "$$is": "##current.id",
        "eq": "##match.id"
      }
    }
  ],
  "to": {
    "*": "##current",
    "e": "##match.e"
  }
}

[
  { 
    "id": 2, 
    "a": 1
  },
  {
    "id": 5,
    "a": 2, 
    "e": true
  }
]

{
    "a1":[
        { "id": "aaa", "val": "a" },
        { "id": "bbb", "val": "b" }
    ],
    "a2": [
        { "name": "aaa", "val": "A" },
        { "name": "bbb", "val": "B" }
    ]
}

{
  "$$lookup": "$.a1",
  "using": [
    {
      "with": "$.a2",
      "as": "a2",
      "on": {
        "$$is": "##current.id",
        "eq": "##a2.name"
      }
    }
  ],
  "to": [ "##current.val", "##a2.val"]
}

[
   [ 
     "a",
     "A" 
   ], 
  [
    "b",
    "B"
  ]
]