Updates values for properties 'a' and 'b' of System with system_id 123.

ExampleMongoDB$SetStatement.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
}
*/

system_states_collection.update(
  { system_id: 123 },
  {
      $set: { a: 4 }
  }
)

/** 
Resulting document: 
{
  system_id: 123,
  a: 4,
  b: 2,
  c: 3
}
*/

system_states_collection.update(
  { system_id: 123 },
  {
      $set: { b: 5 }
  }
)

/** 
Resulting document: 
{
  system_id: 123,
  a: 4,
  b: 5,
  c: 3
}
*/