Automate DynamoDB doc.update call by generating the required attributes from an object literal.

doc-update-partial.js

// Note: This takes your data keys and drops them directly into the 
// UpdateExpression.  If you have more exotic key names, this will likely 
// fail because 'this is a valid key name' works in javascript but not the 
// dynamodb client.  

var keyName = 'thePartitionKey';
var data = { 
  thePartitionKey: '1231342142321321', 
  message: 'your partial data  i.e. the fields you want updated in the target document' 
};

var updateExpressionStatements = [];
var updateExpression;
var expressionAttributeNames = {};
var expressionAttributeValues = {};
Object.keys(data).forEach(function(k) {
  if (k === keyName) return; // skip table keys. they go in a separate param 
  var expressionNameKey = '#' + k;
  var expressionValueKey = ':' + k;
  expressionAttributeNames[expressionNameKey] = k;
  expressionAttributeValues[expressionValueKey] = data[k]
  updateExpressionStatements.push(expressionNameKey + ' = ' + expressionValueKey);
});
updateExpression = 'set ' + updateExpressionStatements.join(', ');
var key = {};
key[keyName] = data[keyName];
var params = {
  UpdateExpression: updateExpression,
  ExpressionAttributeNames: expressionAttributeNames,
  ExpressionAttributeValues: expressionAttributeValues,
  ReturnValues: 'ALL_NEW', 
  Key: key,
};

// ugh.