DynamoDB interpreter

[smacker]

With this PR I want to open a discussion about adding an interpreter for DynamoDB.

References:

• Query.FilterExpression
• Expressions

The code is based on sql package and adapted.

I wonder if it is something you would be interested to merge? What else will we need to add if yes?

[stalniy]

Hey @smacker

First of all, well done! I'm pretty surprised that somebody managed to put own interpreter without much help :) Just wondering how do you plan to use it, together with casl or separately?

I will accept this PR after a bit closer look. Also, I think you need to add somewhere that it's a PartiQL interpreter. At first, for some reason, I expected to see object expressions interpreter.

[smacker]

Thank you. The code is rather simple and straightforward so it is not difficult.

We are planning to use it together with casl. Please take your time, no hurry.

Also, I think you need to add somewhere that it's a PartiQL interpreter

It is not. DynamoDB filter expressions look a lot like PartiQL but they are different. For example, in PartiQL one can write field LIKE '%value' but a filter expression is begins_with(field, 'value') or in PartiQL field IS NULL is a valid syntax but as a filter expression it should be written as attribute_not_exists(field).

The generated values should be passed to DocumentClient.query method as the following:

const dynamo = new DynamoDB.DocumentClient();

const [filterExpr, names, values] = interpret(conditions);
const input: DynamoDB.DocumentClient.QueryInput = {
  FilterExpression: filterExpr,
  ExpressionAttributeNames: names,
  ExpressionAttributeValues: values,
};
const result = await dynamo.query(input).promise();

Keep in mind dynamodb API also contains some deprecated parameters to do the same with a different syntax but they shouldn't be used:

export interface QueryInput {
  /**
   * This is a legacy parameter. Use FilterExpression instead. For more information, see QueryFilter in the Amazon DynamoDB Developer Guide.
   */
  QueryFilter?: FilterConditionMap;
}