Class: Parse::Constraint::ArrayFirstConstraint

Inherits:
Parse::Constraint show all
Defined in:
lib/parse/query/constraints.rb

Overview

Note:

This constraint uses MongoDB aggregation pipeline with $arrayElemAt. While $expr expressions cannot utilize field indexes, aggregation enables positional array access not available in standard Parse queries.

First element constraint - match based on the first element of an array. Uses MongoDB aggregation with $arrayElemAt.

q.where :tags.first => "rock"  # first element equals "rock"

See Also:

Instance Attribute Summary

Attributes inherited from Parse::Constraint

#operand, #operation, #operator, #value

Instance Method Summary collapse

Methods inherited from Parse::Constraint

#as_json, constraint_keyword, create, formatted_value, #formatted_value, #initialize, #key, #precedence, register, #to_s

Constructor Details

This class inherits a constructor from Parse::Constraint

Instance Method Details

#build ⇒ Hash

Returns the compiled constraint using aggregation pipeline.

Returns:

  • (Hash) —

    the compiled constraint using aggregation pipeline.



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# File 'lib/parse/query/constraints.rb', line 1368

def build
  val = formatted_value
  field_name = Parse::Query.format_field(@operation.operand)

  # Handle pointer values. Wrap field reference in $ifNull so a missing
  # field is treated as [] (yielding null from $arrayElemAt) rather than
  # propagating a Missing value through the pipeline.
  if val.respond_to?(:id)
    compare_val = val.id
    pipeline = [
      {
        "$match" => {
          "$expr" => {
            "$eq" => [
              { "$arrayElemAt" => [{ "$map" => {
                  "input" => { "$ifNull" => ["$#{field_name}", []] },
                  "as" => "p",
                  "in" => "$$p.objectId",
                } }, 0] },
              compare_val,
            ],
          },
        },
      },
    ]
  elsif val.is_a?(Parse::Pointer)
    compare_val = val.id
    pipeline = [
      {
        "$match" => {
          "$expr" => {
            "$eq" => [
              { "$arrayElemAt" => [{ "$map" => {
                  "input" => { "$ifNull" => ["$#{field_name}", []] },
                  "as" => "p",
                  "in" => "$$p.objectId",
                } }, 0] },
              compare_val,
            ],
          },
        },
      },
    ]
  else
    pipeline = [
      {
        "$match" => {
          "$expr" => {
            "$eq" => [
              { "$arrayElemAt" => [{ "$ifNull" => ["$#{field_name}", []] }, 0] },
              val,
            ],
          },
        },
      },
    ]
  end

  { "__aggregation_pipeline" => pipeline }
end

#first ⇒ ArrayFirstConstraint

A registered method on a symbol to create the constraint.

Examples:

q.where :tags.first => "rock"

Returns:



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# File 'lib/parse/query/constraints.rb', line 1365

register :first