Parsers

Document Builder exposes the low-level parser functions used internally to build DynamoDB expressions for advanced use-cases. Each parser is a pure function that takes in a specific input type and returns the corresponding DynamoDB expression string along with an AttributeExpressionMap that can be used to get the necessary ExpressionAttributeNames and ExpressionAttributeValues.

Condition Parser

The parseCondition function can be used to parse a Condition object into a DynamoDB ConditionExpression.

const myCondition: Condition = {
  age: greaterThan(21),
  status: equals('active'),
};

const { conditionExpression, attributeExpressionMap } = parseCondition(myCondition);

This returns the ConditionExpression string along with an AttributeExpressionMap that can be used to get the ExpressionAttributeNames and ExpressionAttributeValues.

Alternatively, you can pass an existing AttributeExpressionMap to the parser function as a secondary parameter to reuse an existing map (useful when using multiple parsers together):

const existingMap = new AttributeExpressionMap();

const { conditionExpression } = parseCondition(myCondition, existingMap);

Update Parser

The parseUpdate function can be used to parse an object representing updates into a DynamoDB UpdateExpression.

const myUpdate: UpdateValues = {
  value: 42,
  'nested.attribute': 'newValue',
  counter: increment(1),
};

const { updateExpression, attributeExpressionMap } = parseUpdate(myUpdate);

This returns the UpdateExpression string along with an AttributeExpressionMap that can be used to get the ExpressionAttributeNames and ExpressionAttributeValues.

Alternatively, you can pass an existing AttributeExpressionMap to the parser function as a secondary parameter to reuse an existing map (useful when using multiple parsers together):

const existingMap = new AttributeExpressionMap();

const { updateExpression } = parseUpdate(myUpdate, existingMap);

Projection Parser

The parseProjection function can be used to parse a projection into a DynamoDB ProjectionExpression.

const myProjection: Projection = ['name', 'age', 'address.city'];

const { projectionExpression, attributeExpressionMap } = parseProjection(myProjection);

This returns the ProjectionExpression string along with an AttributeExpressionMap that can be used to get the ExpressionAttributeNames.

Alternatively, you can pass an existing AttributeExpressionMap to the parser function as a secondary parameter to reuse an existing map (useful when using multiple parsers together):

const existingMap = new AttributeExpressionMap();

const { projectionExpression } = parseProjection(myProjection, existingMap);

Tree-shakeable Imports

import { parseCondition } from 'dynamo-document-builder/conditions/condition-parser';
import { parseUpdate } from 'dynamo-document-builder/updates/update-parser';
import { parseProjection } from 'dynamo-document-builder/projections/projection-parser';

API Reference

• parseCondition()
• parseUpdate()
• parseProjection()