Merge pull request #6193 from opentripplanner/ddr_connecti_realay

Add relay connection and global object identification specification guidelines to decision records

DEVELOPMENT_DECISION_RECORDS.md

@@ -110,3 +110,7 @@ Prefer immutable types over mutable. Use builders where appropriate. See
 [Avoid using records if you cannot encapsulate it properly](doc/dev/decisionrecords/RecordsPOJOsBuilders.md#records)
 
 
+## GraphQL Best Practices - API Design
+
+[Follow best practices for designing GraphQL APIs. Our APIs need to be backwards compatible as they are used
+by hundreds of clients (web-pages/apps/services).](doc/dev/decisionrecords/APIGraphQLDesign.md)

doc/dev/decisionrecords/APIGraphQLDesign.md

@@ -0,0 +1,33 @@
+# GraphQL Best Practices - API Design
+
+Follow best practices for designing GraphQL APIs. Our APIs need to be backwards compatible as they
+are used by hundreds of clients (web-pages/apps/services). A good reference used by several
+of the OTP developers is the Production Ready GraphQL book by Marc-André Giroux.
+
+
+## Pagination
+
+We use the [pagination](https://graphql.org/learn/pagination/) (a.k. Relay) specification for paging over entities like stations, 
+stops, trips and routes. Very often OTP has a _finite_ list of entities in memory.
+
+
+## Refetching
+
+We often use `type(id)` format queries for fetching or refetching entities or value objects of type by id. Additionally,
+the GTFS GraphQL API has a node interface and query for refetching objects which follow the
+[GraphQL Global Object Identification Specification](https://relay.dev/graphql/objectidentification.htm). We should not use the
+node interface or query for non-entities (such as Itineraries and Legs) which do not always have an ID and/or which IDs are not
+trivial to reconstruct.
+
+
+## Consistency
+
+Unfortunately, part of the GraphQL API is old and does not follow best practices. So, when adding
+new features, consider what is best; To follow the existing style or follow the best practice. 
+
+
+### Context and Problem Statement
+
+Our APIs need to be backwards compatible as they are used by hundreds of clients (web-pages/apps/services)
+Correcting mistakes may not be possible or may take a long time. 
+

doc/dev/decisionrecords/_TEMPLATE.md

@@ -6,9 +6,6 @@
   document later. 
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-Original pull request: {#NNNN}
-
-
 ### Context and Problem Statement
 
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