Qore Mapper Module Reference: Mapper Module

Qore Mapper Module Reference 1.0

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Mapper Module

# Mapper Module Introduction

This module provides classes that help with structured data mapping, meaning the transformation of data in one or more input formats to a different output format.

Classes provided by this module:

- Mapper: the base data mapping class
- AbstractMapperIterator: an abstract base class for iterator mapper classes
- MapperIterator: a class that automatically applies a data mapper to iterated data

# Mapper Examples

The following is an example map hash with comments:

const DataMap = (
# output field: "id" mapper from the "Id" element of any "^attributes^" hash in the input record
"id": "^attributes^.Id",
# output field: "name": maps from an input field with the same name (no translations are made)
"name": True,
# output field: "explicit_count": maps from the input "Count" field, if any value is present then it is converted to an integer
"explicit_count": ("type": "int", "name": "Count"),
# output field: "implicit_count": runs the given code on the input record and retuns the result, the code returns the number of "Products" sub-records
"implicit_count": int sub (any $ignored, hash $rec) { return $rec.Products.size(); },
# output field: "order_date": converts the "OrderDate" string input field to a date in the specified format
"order_date": ("name": "OrderDate", "date_format": "DD.MM.YYYY HH:mm:SS.us"),
);

If this map is applied to the following data in the following way:

const MapInput = ((
"^attributes^": ("Id": 1),
"name": "John Smith",
"Count": 1,
"OrderDate": "02.01.2014 10:37:45.103948",
"Products": ((
"ProductName": "Widget 1",
"Quantity": 1,
),
)), (
"^attributes^": ("Id": 2),
"name": "Steve Austin",
"Count": 2,
"OrderDate": "04.01.2014 19:21:08.882634",
"Products": ((
"ProductName": "Widget X",
"Quantity": 4,
), (
"ProductName": "Widget 2",
"Quantity": 2,
),
)),
);
my Mapper $map(DataMap);
my list $l = $map.mapAll(MapInput);
printf("%N\n", $l);

The result will be:

    list: (2 elements)
      [0]=hash: (5 members)
        id : 1
        name : "John Smith"
        explicit_count : 1
        implicit_count : 1
        order_date : 2014-01-02 10:37:45.103948 Thu +01:00 (CET)
      [1]=hash: (5 members)
        id : 2
        name : "Steve Austin"
        explicit_count : 2
        implicit_count : 2
        order_date : 2014-01-04 19:21:08.882634 Sat +01:00 (CET))

# Mapper Specification Format

The mapper hash is made up of target (ie output) field names as the key values assigned to field specifications as follows:

- True: this is a shortcut meaning map from an input field with the same name
- a closure or call reference: meaning map from a field of the same name an apply the given code to give the value for the mapping; the closure or call reference must accept the following arguments:
  - any $value: the input field value (with the same name as the output field; to use a different name, see the code hash option below)
  - hash $rec: the current input record
- a hash describing the mapping; the following keys are all optional (an empty hash means map from an input field with the same name with no translations):
  - `"name"`: the value of this key gives the name of the input field; only use this if the input record name is different than the output field name; note that if this value contains `"."` characters and the allow_dot option is not set (see Mapper Options), then the value will be treated like `"struct"`
  - `"struct"`: the value of this key gives the location of the input field in an input hash in dot notation, ex: `"element.name"` would ook for the field's value in the `"name"` key of the `"element"` hash in the input record
  - `"code"`: a closure or call reference to process the field data
  - `"date_format"`: gives the format for converting a string to a date; see date_formatting for the format of this string; note that this also implies `"type"` = `"date"`
  - `"maxlen"`: an integer giving the maximum output string field length in bytes
  - `"trunc"`: assign to boolean True if the field should be truncated if over the maximum field length; this key can only be set to True if the `"maxlen"` key is also given
  - `"mand"`: assign to boolean True if the field is mandatory and an exception should be thrown if no input data is supplied
  - `"type"`: this gives the output field type, can be:
    - `"number"`: field accepts only numeric values (any non-numeric values on input will cause an exception to be thrown when mapping)
    - `"integer"`: fields accepts only integer values (any non-integer values on input will cause an exception to be thrown when mapping; note: also `"int"` is accepted as an alias for `"integer"`)
    - `"date"`: date field

# Mapper Options

Mapper objects accept the following options in the option hash:

- `"enc"`: the output character encoding; if not present then `"UTF-8"` is assumed
- `"name"`: the name of the mapper for use in logging and error strings
- `"trunc"`: an optional closure or call reference for a callback for field truncation warnings; must accept a single string giving the warning text
- `"trunc_all"`: if True (as evaluated by parse_boolean()) then any field without a `"trunc"` key (see Mapper Specification Format `"trunc"` description) will automatically be truncated if a `"maxlen"` attribute is set for the field
- `"allow_dot"`: if True (as evaluated by parse_boolean()) then field names with `"."` characters do not imply a structured internal element lookup; in this case input field names may have `"."` characters in them, use the `"struct"` key to use structured internal element loopups (see Mapper Specification Format `"struct"` docs for more info)
- `"input_log"`: an optional input data logging callback; must accept a hash giving the input data hash
- `"output_log"`: an optional output data logging callback; must accept a hash giving the output data hash

# Release Notes

## Mapper v1.0

Initial release.