Misc Operators

Besides the main categories of operators, ReductStore supports a few miscellaneous operators that provide additional functionality:

Operator	Description
$exists	Checks if a label exists in a record.
$cast	Casts a label value to a different type explicitly.
$ref	References a label value in a record explicitly.

$exists

The $exists operator is used to check if a label exists in a record.

The operator is useful when you want to filter records based on the presence of a label, regardless of its value.

Syntax

{
  "$exists": [ <expression as label reference> ]
}

Behavior

The operator evaluates the first expression as a string and checks if the label exists in the record.

Additional rules:

• If the expression is not a string, it is cast to a string.
• The operator is case-sensitive.

Examples

Array notation:

{
  "$exists": ["label_name"]
}

$cast

The $cast operator is used to cast a label value to a different type explicitly.

The condition query engine automatically casts values to the correct type when comparing them, but sometimes you may want to cast a value explicitly.

Syntax

{
  "$cast": [ <expression as label reference>, <"bool" | "int" | "float" | "string"> ]
}

Behavior

The operator evaluates the first expression then casts the value to the specified type in the second argument.

Supported types:

• bool: Casts the value to a boolean.
• int: Casts the value to an integer.
• float: Casts the value to a float.
• string: Casts the value to a string.

Examples

Object notation:

{
  "$cast": {
    "&label_name": "int"
  }
}

Array notation:

{
  "$cast": ["&label_name", "int"]
}

$ref

The $ref operator is used to reference a label value in a record explicitly.

This is equivalent to using the label reference "&" in the query object, however, it allows you to use expressions to reference labels.

Syntax

{
  "$ref": [ <expression as label reference> ]
}

Behavior

The operator evaluates the first expression as a string and references the label value in the record.

Examples

Simple reference to a label:

{
  "$ref": ["label_name"]
}

Using an expression to reference a label:

{
  "$ref": [{ "$concat": ["label_", "name"] }]
}