Have multiple single view creator for one single view

The update strategy provides a way to divide the aggregation effort of a Single View between more than one Single View Creator.

tip

This is specially useful when one of the computation efforts is much bigger than the other so it makes sense to dedicate a Single View Creator with more resources to deal with the workload and not block the queue for what could be faster aggregations.

Use Case

For example, we have a Single View called sv_posts, with a base projection called posts having a one to many relationship to comments:

sv_posts

{
  title: string,
  comments: {text: string}[]
}

Services Configuration

Linking two services from the Single View section, we can have two Single View Creators, namely svc-1 and svc-2 each one configured with the update strategy: in this way, svc-1 will be in charge of handling just the title field, while svc-2 will compute just the comments array.

Write the aggregation

The aggregation.json files would look like that:

svc-1-aggregation.json

{
  "version": "1.3.0",
   "config": {
      "SV_CONFIG": {
         "dependencies": {
            "posts": {
               "type": "projection",
               "on": "_identifier",
            },
         },
         "mapping": {
            "title":"posts.title"
         }
      }
   }
}

svc-2-aggregation.json

{
   "version": "1.3.0",
   "config": {
      "SV_CONFIG": {
         "dependencies": {
            "posts": {
               "type": "projection",
               "on": "_identifier"
            },
            "COMMENTS": {
               "type": "config"
            }
         },
         "mapping": {
            "comments": "COMMENTS"
         }
      },
      "COMMENTS": {
         "dependencies": {
            "comments": {
               "on": "posts_to_comments",
               "type": "projection"
            }
         },
         "joinDependency": "comments",
         "mapping": {
            "text": "comments.text"
         }
      }
   }
}

So, at the end we will have the first Single View Creator with the first aggregation.json ( svc-1-aggregation.json ) above and the UPSERT_STRATEGY set to update. And the second Single View Creator with the second aggregation.json ( svc-2-aggregation.json ) and the UPSERT_STRATEGY also set to update.

Strategy definition

Once both aggregations are defined, we have to assign each projection's strategy to the corresponding single view creator. In particular

• svc-1 has to receive projection changes from posts strategy;
• svc-2 has to receive projection changes from comments strategy.

This can be achieved by using two different TYPE environment variables for the two services, for example:

• TYPE: svc-1 will be used by micro-service svc-1;
• TYPE: svc-2 will be used by micro-service svc-2

After defining the type, you can assign to each strategy the type attribute in the Strategy section