Entigen

Meta-model entity generator

Generator that takes an entity-relationship-like model as input and generates various blocks of source files that either describe the model in the target language or perform some functionality with the structures of the model.

The tool's goals are:

• Reduce boilerplate while maintaining transparency
• Reduce points where error might be manually introduced
• Respect multiple languages and preserve type consistency

Example uses: class definition, initialization methods, comparators, database storage/retrieval operations, protocol specifications, documentation, etc.

This tool is to be used when language magic is not desired and when transparent code and ability to diagnose is prefered. Examples of language magic: Python metaclasses, synthesized properties and methods.

Requirements

The entigen tool requires Python >= 3.6

Usage

usage: entigen [-h] [-b BLOCK_TYPE] [-f READER] [-t WRITER] [-V VARIABLES]
			   model [entities [entities ...]]

Process some integers.

positional arguments:
  model                 Model source
  entities              Entities to be included

optional arguments:
  -h, --help            show this help message and exit
  -b BLOCK_TYPE, --block BLOCK_TYPE
						Block type the writer writes
  -f READER, --from READER
						Metamodel input format
  -t WRITER, --to WRITER
						Text output format
  -V VARIABLES, --variable VARIABLES
						Text output format

Example: go to the examples directory and run:

entigen thing.model > thing.py

Then see the generated thing.py file.

Writers and Blocks

The following writers are available:

• python – Python source file or snippet writer
• info – Text output writer

Python Writer

The Python writer writes type-annotated Python 3.6 source code. Blocks:

• class – class with instance variable annotations and the __init__ and __eq__ method
• class_file – file with classes of specified entities
• enums_file – file with definitions of all enums

__init__ – method takes one argument per entity property and then assigns it to the corresponding instance variable. If a variable is composite, such as list, and has a default value, then the default value is assigned within the method, not in the argument list.

__eq__ – method takes other object, then compares whether the other object is of the same subclass as the entity. All properties of the entity are compared with the properties of the other entity.

Variables:

• entities_module – module name from which entities are imported
• entity_per_module - if set to true, then every entity imported has it's own sub-module within the entities_module. For example, if entity d ImportantThing is required, and the entities module is entities then the import will be from entities.important_thing import ImportantThing
• enums_module – module from which enums are imported

Info Writer

The info writer can be used by shell scripts to learn more about the moden and the have better control over overal output generation using other writers.

To list names of all entities in a model, one per line, use:

entigen -w info model

Variables:

• decamelize – write entity names as lower-case identifiers

Readers

The default reader is a csv reader. The meta-model is a directory with CSV files describing meta-model entities. Files:

• properties.csv – list of entity properties. Fields: category, entity, name, type, optional, tag, label, description
• entities.csv – list of entities.

The main reason for the CSV input format is that it is structured and can be edited as text or as a spreadsheet. Spreadsheet applications are wide-spread enough and they have quite comfortable user interface for editing structured data.

Data Types

The generator comes with it's own very simple data types. The variety of types is intentionally limited so we are able to cover wide variety of outputs with easy type and type handling translation.

The base types are:

• string
• int
• identifier - internally same as string, but writers can implement checks for content beign valid identifier
• objref - object reference – interpretation left to application or writer. Usually Any or object type, in database it might be just integer or uuid

The complex types are:

• list<BASETYPE1,BASETYPE2,...> - list of base-type objects

Special default values

The following special values should be compared as whole strings for their corresponding types.

• [] is a special default value for a string meaning an empty list

Development

Some things to keep in mind while working on this tool:

• The generated source should be as human-readable as possible, it should be nicely formatted and not far from how a person with a good style would write it.
• When adding a core data type its availability or convertibility to other languages (programming or modelling) should be strongly considered.

Author and License

Author: Stefan Urbanek stefan.urbanek@gmail.com

License: MIT