Queries
The third type of Message that an Axon application is associated with is the Query Message, or simply Queries. These are messages that request information in a certain format. Any application can declare it’s able to handle a query message, and provide a response to it.
Types of queries
There are multiple types of queries that cane be distinguished.
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Point-to-point queries: They are routed to a single handler, which is expected to return a single result. This is the most common type of query.
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Scatter-gather queries: These queries are dispatched to all handlers that are capable of handling the query. The results of all handlers are then aggregated and returned to the client.
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Subscription queries: These request an initial result and then continue to receive updates as long as the subscription is active.
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Streaming queries: These queries are used to request a stream of results, which are returned as they become available.
You can find more about each type of query in the Query Dispatchers section.
Subsections
A summary of the various sections is given below.
| Subsection | Purpose |
|---|---|
Functional Development concerns for Query Messages using the Axon Framework |
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Non-Functional Development concerns for Query Messages using the Axon Framework |
|
Configuration concerns for Query Messages using the Axon Framework |
This guide is complemented by a video tutorial which gives a practical demonstration of the concepts explained in this section. The tutorial is available at -> Axon Coding Tutorial - Query Messages