mapry 1.0.0.3

Documentation

This document gives only a brief summary of Mapry. The full documentation can be found here.

Introduction

Let us introduce Mapry here by presenting a short example in order to give you a first impression on how the generator can be used. To get the full picture, please consult the documentation.

The schema starts with the name and a description, followed by the language-specific settings (specifying the non-standard parts of the code generation), the definition of the graph structure and finally the definition of the properties of the object graph itself.

Here is an example schema to give you an overview:

{
  "name": "Pipeline",
  "description": "defines an address book.",
  "cpp": {
    "namespace": "book::address",
    "path_as": "boost::filesystem::path",
    "optional_as": "std::experimental::optional",
    "datetime_library": "ctime"
  },
  "go": {
    "package": "address"
  },
  "py": {
    "module_name": "book.address",
    "path_as": "pathlib.Path",
    "timezone_as": "pytz.timezone"
  },
  "classes": [
    {
      "name": "Person",
      "description": "defines a contactable person.",
      "properties": {
        "full_name": {
          "type": "string",
          "description": "gives the full name (including middle names)."
        },
        "birthday": {
          "type": "date",
          "description": "indicates the birthday in UTC."
        },
        "address": {
          "type": "Address",
          "description": "notes where the person lives."
        }
      }
    }
  ],
  "embeds": [
    {
      "name": "Address",
      "description": "defines an address.",
      "properties": {
        "text": {
          "type": "string",
          "description": "gives the full address."
        }
      }
    }
  ],
  "properties": {
    "maintainer": {
      "type": "Person",
      "description": "indicates the maintainer of the address book."
    }
  }
}

Once you generated the de/serialization code with Mapry, you can use it to obtain the object graph from a JSONable.

For example, assume a JSONable stored in /path/to/the/file.json:

{
  "persons": {
    "alice": {
      "full_name": "Alice Doe",
      "birthday": "1983-10-24",
      "address": {
        "text": "Some street 12, Some City, Some Country"
      }
    },
    "bob": {
      "full_name": "Bob Johnson",
      "birthday": "2016-07-03",
      "address": {
        "text": "Another street 36, Another City, Another Country"
      }
    }
  },
  "maintainer": "alice"
}

You can parse the object graph in, say, Python:

# Obtain a JSONable
pth = '/path/to/the/file.json'
with open(pth, 'rt') as fid:
    value = json.load(fid)

# Parse the JSONable
errors = book.address.parse.Errors(cap=10)

pipeline = book.address.fromjsonable.pipeline_from(
    value=value,
    ref=pth + '#',
    errors=errors)

if not errors.empty():
    for error in errors.values():
        print("{}: {}".format(error.ref, error.message), file=sys.stderr)

    return 1

and access the object graph as pipeline:

print('Persons are:')
for person in pipeline.persons:
    print('{} (full name: {}, address: {}, birthday: {})'.format(
        person.id,
        person.full_name,
        person.address.text,
        person.birthday.strftime("%d.%m.%Y")))

print('The maintainer is: {}'.format(
    pipeline.maintainer.id))

The generated code for this schema can be downloaded for C++, Go and Python.

Usage

Mapry provides a single point-of-entry for all code generation through mapry-to command.

To generate the code in different languages, invoke:

For C++:

mapry-to cpp \
    --schema /path/to/schema.json \
    --outdir /path/to/cpp/code

For Go:

mapry-to go \
    --schema /path/to/schema.json \
    --outdir /path/to/go/code

For Python:

mapry-to py \
    --schema /path/to/schema.json \
    --outdir /path/to/py/code

If the output directory does not exist, it will be created. Any existing files will be silently overwritten.

Installation

We provide a prepackaged PEX file that can be readily downloaded and executed. Please see the Releases section.

If you prefer to use Mapry as a library (e.g., as part of your Python-based build system), install it with pip:

pip3 install mapry

Contributing

All contributions are highly welcome. Please consult this page in the documentation to see how you can contribute.

Versioning

We follow Semantic Versioning. We extended the standard semantic versioning with an additional format version. The version W.X.Y.Z indicates:

• W is the format version (data representation is backward-incompatible),

• X is the major version (library interface is backward-incompatible),

• Y is the minor version (library interface is extended, but backward-compatible), and

• Z is the patch version (backward-compatible bug fix).

Related Projects

We compiled an extensive list of related projects and how they compare to Mapry in the documentation.

We present here only the most prominent projects and their main differences to Mapry:

Standard JSON libraries

support only object trees, not graphs. They usually lack a schema (e.g., json module in Python).

De/serializers based on annotations

handle object graphs through custom logic (e.g., Jackson in Java). Since they are based on annotations in source code, a polyglot code base would require a duplication across different languages which can be cumbersome and error-prone to keep synchronized.

Standard or widely used serialization libraries

handle object graphs well and provide a rich set of primitives. However, the serialization format differs accross languagues (e.g., Boost.Serialization in C++ or Pickle in Python would need to be supported in Go).

Popular serializers based on generated code

usually do not de/serialize object graphs, but only object trees (e.g., Protocol Buffers or Cap’n Proto).

Flatbuffers being the exception handle object graphs natively, but lack support for sophisticated types such as maps and datetimes, durations etc.