Shows how we can choose to only update documents with older values of our property using timestamps

ExampleMongoDBUpdateStatementUsingLastModified.ts

/** create connection pool to system DB in MongoDB
* assume we are using https://www.npmjs.com/package/mongodb
* assume we begin with:
{
  system_id: 123,
  a: 1,
  b: 2,
  c: 3,
  last_modified: {
    a: '2020-03-10T10:33:13.012Z'
  }
}

Receive new state with the following data:
{
  system_id: 123,
  a: 4,
  published: '2020-03-10T10:33:43.012Z'
}
*/

system_states_collection.update(
  // find document with timestamp for 'a' less than or equal to our timestamp
   { system_id: 123, 'last.modified.a': { $lte: Date('2020-03-10T10:33:43.012Z') }, 
   {
      $set: { 
        a: 4,
        'last_modified.a': Date('2020-03-10T10:33:43.012Z')
      },
   }
) 
/**
* Document will only be updated if it finds a document with a 
* value for property 'last_modified.a' less than or equal to our 
* timestamp (which is the published time of the update from our source)
*/

/** 
Resulting document: 
{
  system_id: 123,
  a: 4,
  b: 2,
  c: 3,
  last_modified: {
    a: '2020-03-10T10:33:43.012Z'
  }
}
*/