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Layer-ServiceAgent.md

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Service Agent

The Service Agent is the proxy layer that encapsulates the invocation of the corresponding Service Interface layer.

This layer is code-generated and responsible for performing the HTTP request / response handling.


Capabilities

The TypedHttpClientBase provides the core Service Agent functionality for invoking an API endpoint using HTTP:

  • GetAsync - HTTP GET - generally a Read (CRUD) operation.
  • PutAsync - HTTP PUT - generally a Create (CRUD) operation.
  • PostAsync - HTTP POST - generally an Update (CRUD) replacement operation.
  • PatchAsync - HTTP PATCH - generally an Update (CRUD) modification operation.
  • Delete - HTTP DELETE - generally a Delete (CRUD) operation.

The following is generally performed for each:

Step Description
Request Create the HttpRequestMessage.
RequestUri Set the HttpRequestMessage.RequestUri including the query string.
ETag Where there is an HttpRequestOptions.ETag this will result in an If-None-Match (GET) or alternatively If-Match header.
Serialize Serializes the entity (where specified) as JSON to the HttpRequestMessage.Content as applicable.
Send Uses an underlying HttpClient to send the HttpRequestMessage using the specified HTTP Method.
Response Accepts the corresponding HttpResponseMessage.
StatusCode Where the HttpResponseMessage.IsSuccessStatusCode is true, will deserialize the JSON HttpResponseMessage.Content as the resulting entity; otherwise, will convert the HttpResponseMessage.StatusCode to the equivalent IExtendedException and throw.

Usage

There is a generated class per Entity named {Entity}Agent. There is also a corresonding interface named I{Entity}Agent generated so the likes of test mocking etc. can be employed. For example, if the entity is named Person, there will be corresponding PersonAgent and IPersonAgent classes.

There are currently no opportunities for a developer to extend on the generated code; beyond amending the underlying code generation templates. This is by design to limit the introduction of business or data logic into this layer.


Request manipulation

However, there will more often than not be the need to manipulte the request. For example, add the likes of the credentials for authentication as part of the request before send. There are multiple opportunities to perform this; select the best method based on the requirements:

  • DelegatingHandler - allows standardized request logic to be used for any HttpClient.SendAsync. This article, and the two preceeding within, provide the details on how to achieve.
  • Fluent OnBeforeRequest - the DefaultOptions.OnBeforeRequest fluent-style method can be used to set for the instance.
  • Override OnBeforeRequest - as the {Entity}Agent is implemented as a partial class this can be extended by overridding the default protected OnBeforeRequest method and the requistite logic included.