Aggregating data to a list

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Example Events
A common use-case is collecting some data across all aggregates for a given type. In the example below we want to be able to get a list of all registered Customers from a single query to a Projection.
Let's say two Customers have been registered in our system with the following two events:
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  {  
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     "aggregateId":"723ecfce-14e9-4889-98d5-a3d0ad54912f",
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     "events":[  
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        {  
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           "eventId":"127b80b5-4a05-4774-b870-1c9a2e2a27a3",
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           "eventType":"CustomerRegisteredEvent",
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           "data":{  
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              "customer": "Acme Inc"
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           }
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        }
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     ]
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  }
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  {  
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     "aggregateId":"cf26e6df-a883-4fbc-929b-47052f0acdb8",
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     "events":[  
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        {  
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           "eventId":"982f8747-ba7d-470e-beca-1582c48d3181",
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           "eventType":"CustomerRegisteredEvent",
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           "data":{  
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              "customer": "The Trading Company"
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           }
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        }
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     ]
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  }
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Projection definition
We can create an aggregated Projection that appends all Customer names to a field in our Aggregated Projection called registered-customers.
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{
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  "aggregated": true,
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  "projectionName": "registered-customers",
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  "feedName": "customer",
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  "handlers": [
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    {
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      "eventType": "CustomerRegisteredEvent",
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      "functions": [
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        {
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          "function": "append",
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          "eventSelector": "$.event.customer",
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          "targetSelector": "$.projection.customers"
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        }
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      ]
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    }
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  ]
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}
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Results
When we query the Aggregated Projection we will now get the following result.
/projections/aggregated/registered-customers
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{
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  "projectionId" : "registered-customers",       
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  "createdAt" : 1523518145532,                                   
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  "updatedAt" : 1523518146253,                                   
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  "data": {
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    "customers": ["Acme Inc", "The Trading Company"]
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  }
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}
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Adding filter support to Projections
Adding and removing from lists
Last modified 1yr ago
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Contents
Example Events
Projection definition
Results