Misc Operators

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

Operator	ReductStore Version	Description
$has | $exists	v1.14	Checks if a record has specific labels.
$cast	v1.14	Casts a label value to a different type explicitly.
$ref	v1.14	References a label value in a record explicitly.
$timestamp | $id	v1.15	Retrieves the timestamp of a record as a UNIX time in microseconds.

$has | $exists

The $has or $exists operator is used to check if a record has specific labels.

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

Syntax

{
  "$has" | "$exists" : [ <expression as label reference>, ... ]
}

Behavior

The operator evaluates expressions as strings and checks if the record has all the specified labels.

Additional rules:

• If the expression is not a string, it is cast to a string.
• The operator is case-sensitive.
• The evaluation stops as soon as one of the labels is not found.

Examples

Check if a record has labels label_1 and label_2:

{
  "$has": ["label_1", "label_2"]
}

$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" | "duration"> ]
}

Behavior

The operator evaluates the first expression then casts the value to the specified type in the second argument. Supported types are: bool, int, float, string, and duration. See the casting rules for more details.

Examples

Object notation:

{
  "$label_name": {
    "$cast": "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:

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

$timestamp | $id

The $timestamp operator is used to retrieve the timestamp of a record as a UNIX time in microseconds. The operator is useful when you want to filter records based on their timestamp or when you want to use the timestamp in calculations.

Syntax

{
  "$timestamp": []
}

Behavior

The operator is a nullary operator that returns the timestamp of the record as a UNIX time in microseconds.

Examples

Retrieve a certain record by its timestamp:

{
  "$timestamp": { "$eq": 1672531199000 }
}

Retrieve multiple records by their timestamps:

{
  "$in": ["$timestamp", 1672531199000, 1672531200000]
}