Transpilers for building BSON documents in any language. Current support provided for shell as inputs. java, c#, node, shell, python, ruby and go as outputs.

See also the original presentation: https://drive.google.com/file/d/1jvwtR3k9oBUzIjL4z_VtpHvdWahfcjTK/view

NOTES:

1. A version of the code with support for python with corresponding test cases has been removed to avoid bundling and supporting unused code, however it can be still be found in https://github.com/mongodb-js/compass/tree/80cf701e44cd966207f956fac69e8233861b1cd5/packages/bson-transpilers.
2. The shell output is disabled as is essentially the only input in use and it produces code that is compatible only with legacy mongo shell not the new mongosh shell. See COMPASS-4930 for some additional context.

const transpiler = require('bson-transpilers');

const input = 'shell';
const output = 'java';

const string =`
{ item: "book", qty: Int32(10), tags: ["red", "blank"], dim_cm: [14, Int32("81")] }`;

try {
  const compiledString = transpiler[input][output].compile(string);
  console.log(compiledCode);
  // new Document("item", "book").append("qty", 10)
  // .append("tags", Arrays.asList("red", "blank"))
  // .append("dim_cm", Arrays.asList(14L, 81")))
} catch (error) {
  console.error(error);
}

Output a compiled string given input and output languages.

• inputLang: Input language of the code string. shell and javascript are currently supported.
• outputLang: The language you would like the output to be. java, python, shell, javascript, and csharp are currently supported.
• codeString: The code string you would like to be compiled to your selected output language.

Output a string containing the set of import statements for the generated code to compile. These are all the packages that the compiled code could use so that the transpiler output will be runnable.

• inputLang: Input language of the code string. shell and javascript are currently supported.
• outputLang: The language you would like the output to be. java, python, shell, javascript, and csharp are currently supported.
• mode: Either 'Query' for the .find() method or 'Pipeline' for .aggregate().
• driverSyntax: Whether or not you want to include Driver Syntax into your output string.

Any transpiler errors that occur will be thrown. To catch them, wrap the transpiler in a try/catch block.

• error.message: Message bson-transpilers will send back letting you know the transpiler error.
• error.stack: The usual error stacktrace.
• error.code: Error code that bson-transpilers adds to the error object to help you distinguish error types.
• error.line: If it is a syntax error, will have the line.
• error.column: If it is a syntax error, will have the column.
• error.symbol: If it is a syntax error, will have the symbol associated with the error.

The CodeGenerationVisitor class manages a global state which is bound to the argsTemplate functions. This state is intended to be used as a solution for the argsTemplate functions to communicate with the DriverTemplate function. For example:

ObjectIdEqualsArgsTemplate: &ObjectIdEqualsArgsTemplate !!js/function >
    (_) => {
        this.oneLineStatement = "Hello World";
        return '';
    }

DriverTemplate: &DriverTemplate !!js/function >
    (_spec) => {
      return this.oneLineStatement;
    }

The output of the driver syntax for this language will be the one-line statement Hello World.

A more practical use-case of state is to accumulate variable declarations throughout the argsTemplate to be rendered by the DriverTemplate. That is, the motivation for using DeclarationStore is to prepend the driver syntax with variable declarations rather than using non-idiomatic solutions such as closures.

The DeclarationStore class maintains an internal state concerning variable declarations. For example,

// within the args template
(arg) => {
  return this.declarations.add("Temp", "objectID", (varName) => {
    return [
      `${varName}, err := primitive.ObjectIDFromHex(${arg})`,
      'if err != nil {',
      '   log.Fatal(err)',
      '}'
    ].join('\n')
  })
}

Note that each use of the same variable name will result in an increment being added to the declaration statement. For example, if the variable name objectIDForTemp is used two times the resulting declaration statements will use objectIDForTemp for the first declaration and objectID2ForTemp for the second declaration. The add method returns the incremented variable name, and is therefore what would be expected as the right-hand side of the statement defined by the argsTemplate function.

The instance of the DeclarationStore constructed by the transpiler class is passed into the driver, syntax via state, for use:

(spec) => {
  const comment = '// some comment'
  const client = 'client, err := mongo.Connect(context.Background(), options.Client().ApplyURI(cs.String()))'
  return "#{comment}\n\n#{client}\n\n${this.declarations.toString()}"
}

There are a few different error classes thrown by bson-transpilers, each with their own error code:

This will occur when you're using a method with a wrong number of arguments, or the arguments are of the wrong type. For example, ObjectId().equals() requires one argument and it will throw if anything other than one argument is provided:

// ✘: this will throw a BsonTranspilersArgumentError.
ObjectId().equals(ObjectId(), ObjectId());

// ✔: this won't throw
ObjectId().equals(ObjectId());

// ✘: this will throw a BsonTranspilersArgumentError.
ObjectId({});

// ✔: this won't throw
ObjectId();

Will be thrown if an invalid method or property is used on a BSON object. For example, since new DBRef() doesn't have a method .foo(), transpiler will throw:

// ✘: method foo doesn't exist, so this will throw a BsonTranspilersAttributeError .
new DBRef('newCollection', new ObjectId()).foo()

// ✔: this won't throw, since .toString() method exists
new DBRef('newCollection', new ObjectId()).toString(10)

This will throw if you have a syntax error. For example missing a colon in Object assignment, or forgetting a comma in array definition:

// ✘: this is not a proper object definition; will throw E_SYNTAX_GENERIC
{ key 'beep' }

// ✘: this is not a proper array definition, will throw E_SYNTAX_GENERIC
[ 'beep'; 'boop' 'beepBoop' ]

// ✔: neither of these will throw
{ key: 'beep' }
[ 'beep', 'boop', 'beepBoop' ]

This error will occur if a symbol is treated as the wrong type. For example, if a non-function is called:

// ✘: MAX_VALUE is a constant, not a function
Long.MAX_VALUE()

// ✔: MAX_VALUE without a call will not throw
Long.MAX_VALUE

If there is a feature in the input code that is not currently supported by the transpiler.

A generic runtime error will be thrown for all errors that are not covered by the above list of errors. These are usually constructor requirements, for example when using a RegExp() an unsupported flag is given:

// ✘: these are not proper 'RegExp()' flags, a BsonTranspilersRuntimeError will be thrown.
new RegExp('ab+c', 'beep')

// ✔: 'im' are proper 'RegExp()' flags
new RegExp('ab+c', 'im')

In the case where something has gone wrong within compilation, and an error has occured. If you see this error, please create an issue on Github!

npm install -S bson-transpilers

Head over to the readme on contributing to find out more information on project structure and setting up your environment.

• aherlihy - Anna Herlihy herlihyap@gmail.com
• alenakhineika - Alena Khineika alena.khineika@mongodb.com
• lrlna - Irina Shestak shestak.irina@gmail.com

Apache-2.0