$$lookup

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

Usage

{ 
  "$$lookup": [ /* Main array of elements */ ],
  "using": [ /* array */
    {
      "with": /* array */,
      "as": /* string */,
      "on": /* Transformer(##current,##index,##{as}) */,
    },
    ...
  ],
  "to": /* Transformer(##current,##{as},...) */
}

"$$lookup(<using>,[to]):{input}"

{
  "$$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		Yes	Main array of elements
using	array		Yes	Array of definitions of how to match other arrays to the main one
to	Transformer(##current,##{as},...)		null	Transformer to map each pair of elements to its value in the result array  Default behavior is to merge ##current with ##\{as} (append & overwrite) ##current - Current element ##{as} - Matched element from with ... -
using[].with	array		Yes	Array of elements to match with
using[].as	string		Yes	The name the elements from this entry will be referred as (#\{as})
using[].on	Transformer(##current,##index,##{as})		Yes	Evaluated condition on when to match an element from the main array and with array (uses the Truthy logic) ##current - Current element ##index - Current index ##{as} - the matched element from the array (replace \{as} with the name provided in as argument)

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
  }
]

Test

{
  "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
  }
]

Test

{
  "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
  }
]

Test

{
  "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"
  ]
]

Test