OData V2 vs V4 $metadata, side by side

Many SAP Gateway services still speak OData V2, while new services (RAP, CAP, ASP.NET Core) default to V4. The data model is the same idea in both — entity types, keys, properties, entity sets — but the $metadata document spells relationships and operations differently. Open both Northwind services and compare: Northwind V2 and Northwind V4.

Topic	V2 (EDMX 1.0)	V4 (EDMX 4.0 / CSDL JSON)
Envelope	`edmx:Edmx Version="1.0"`, `m:DataServiceVersion="2.0"`	`edmx:Edmx Version="4.0"`
Relationships	`Association` + `AssociationSet`, navigation via `Relationship`/`FromRole`/`ToRole`	`NavigationProperty Type="NS.T"` or `Collection(NS.T)`, `Partner`, `ReferentialConstraint` on the property
Bindings	Association sets connect two entity sets	`NavigationPropertyBinding Path=… Target=…` in the entity set
Operations	`FunctionImport` with `m:HttpMethod`	`Function` / `Action` (bound or unbound) + `FunctionImport` / `ActionImport`
Annotations	`sap:label`, `sap:creatable`, … as XML attributes	`Annotation Term="Common.Label"`, vocabularies, external `Annotations Target=…`
Count	`$inlinecount=allpages`, `/$count`	`$count=true`
JSON answer	`{"d": {"results": [...], "__count": "…"}}`	`{"value": [...], "@odata.count": …}`
Dates	`/Date(1700000000000)/`	ISO 8601 `2026-10-19T08:00:00Z`
Containment, singletons, enums	—	yes

What the viewer does with the difference

It reads both into one model: V2 associations become navigation properties with multiplicity on both ends, association sets become navigation bindings, function imports appear as operations, and sap: attributes are listed as annotations next to the V4 vocabulary terms. The ER diagram therefore looks the same for both versions, which makes a migration check quick: load the old and the new service in two tabs and compare entity by entity.

Migrating clients

Replace $inlinecount with $count=true and read @odata.count.
substringof('x',Name) becomes contains(Name,'x').
Date literals lose the datetime'…' prefix.
Deferred navigation links (__deferred) are gone; use $expand or follow the navigation URL.

Open Northwind V2