Class: Parse::Constraint::PointerEqualsLinkedPointerConstraint

Inherits:

Parse::Constraint

Object
Parse::Constraint
Parse::Constraint::PointerEqualsLinkedPointerConstraint

show all

Defined in:: lib/parse/query/constraints.rb

Overview

A constraint for comparing pointer fields through linked objects using MongoDB aggregation. This allows comparing ObjectA.field1 with ObjectA.linkedObject.field2 where both are pointers.

# Find ObjectA where ObjectA.author equals ObjectA.project.owner ObjectA.where(:author.equals_linked_pointer => { through: :project, field: :owner })

# This generates a MongoDB aggregation pipeline with $lookup and $expr # to compare pointer fields across linked documents

Instance Attribute Summary

Attributes inherited from Parse::Constraint

#operand, #operation, #operator, #value

Instance Method Summary collapse

#build ⇒ Hash
The compiled constraint.
#equals_linked_pointer ⇒ PointerEqualsLinkedPointerConstraint
A registered method on a symbol to create the constraint.

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.

Returns:

(Hash) —
the compiled constraint.

# File 'lib/parse/query/constraints.rb', line 2842

def build
  unless @value.is_a?(Hash) && @value[:through] && @value[:field]
    raise ArgumentError, "equals_linked_pointer requires: { through: :linked_field, field: :target_field }"
  end

  through_field = @value[:through]
  target_field = @value[:field]
  local_field = @operation.operand

  # Format field names according to Parse conventions
  # Pointer fields in MongoDB are stored with _p_ prefix
  formatted_through = "_p_" + Parse::Query.format_field(through_field)
  formatted_target = "_p_" + Parse::Query.format_field(target_field)
  formatted_local = "_p_" + Parse::Query.format_field(local_field)

  # Determine the target collection name from the through field
  # Use classify to convert field name to class name (e.g., :project -> "Project")
  target_collection = through_field.to_s.classify

  # Build the aggregation pipeline
  # Use clean alias name without _p_ prefix for readability
  lookup_alias = "#{through_field.to_s.camelize(:lower)}_data"

  # Parse stores pointers as "ClassName$objectId" strings
  # We need to extract just the objectId part after the $
  pipeline = [
    {
      "$addFields" => {
        "#{formatted_through}_id" => {
          "$substr" => [
            "$#{formatted_through}",
            target_collection.length + 1,  # Skip "ClassName$"
            -1,  # Rest of string
          ],
        },
      },
    },
    {
      "$lookup" => {
        "from" => target_collection,
        "localField" => formatted_through,
        "foreignField" => "_id",
        "as" => lookup_alias,
      },
    },
    {
      "$match" => {
        "$expr" => {
          "$eq" => [
            { "$arrayElemAt" => ["$#{lookup_alias}.#{formatted_target}", 0] },
            "$#{formatted_local}",
          ],
        },
      },
    },
  ]

  # Return a special marker that indicates this needs aggregation pipeline processing
  { "__aggregation_pipeline" => pipeline }
end

#equals_linked_pointer ⇒ `PointerEqualsLinkedPointerConstraint`

A registered method on a symbol to create the constraint.

Examples:

q.where :field.equals_linked_pointer => { through: :linked_field, field: :target_field }