fix!: use Java types for scalar schemas

README.md

@@ -177,7 +177,7 @@ String readerId =
             () ->
                 client.readers().list(merchantCode).items().stream()
                     .findFirst()
-                    .map(reader -> reader.id().value())
+                    .map(reader -> reader.id())
                     .orElseThrow(() -> new IllegalStateException("No paired readers found.")));
 
 CreateReaderCheckoutRequest request =
@@ -224,7 +224,7 @@ CompletableFuture<String> readerIdFuture =
                         response ->
                             response.items().stream()
                                 .findFirst()
-                                .map(reader -> reader.id().value())
+                                .map(reader -> reader.id())
                                 .orElseThrow(
                                     () ->
                                         new IllegalStateException("No paired readers found."))));

codegen/README.md

@@ -22,6 +22,12 @@ just generate
 
 The command is idempotent; rerunning it rewrites the generated clients in-place. Continuous Integration runs the same invocation and fails when the working tree is dirty afterward.
 
+Named scalar schemas use the same Java types as inline schemas: `String`, boxed
+numbers and booleans, or the existing date/time and UUID format mappings. They do
+not generate wrapper records. Enum schemas retain their open enum classes, and
+structured schemas retain their models. This applies to parameters, request and
+response fields, and code samples.
+
 ## Java Code Samples
 
 The `samples` command generates a deterministic, versioned JSON catalog of Java examples from the same intermediate representation used to generate the SDK. Each catalog entry contains a complete Java program. Named OpenAPI request examples produce separate entries.

codegen/internal/generator/additional_properties_test.go

@@ -107,16 +107,7 @@ func TestGenerateModelWithoutBuilderForTypeAliases(t *testing.T) {
 	}
 
 	lonPath := filepath.Join(outputDir, "com", "test", "sdk", "models", "Lon.java")
-	lonContent, err := os.ReadFile(lonPath)
-	if err != nil {
-		t.Fatalf("read generated Lon model: %v", err)
-	}
-	lonGenerated := string(lonContent)
-
-	assertContains(t, lonGenerated, "public record Lon(")
-	assertContains(t, lonGenerated, "Float value")
-	assertNotContains(t, lonGenerated, "public static Builder builder()")
-	assertNotContains(t, lonGenerated, "public static final class Builder")
+	assertFileDoesNotExist(t, lonPath)
 
 	metaPath := filepath.Join(outputDir, "com", "test", "sdk", "models", "Meta.java")
 	metaContent, err := os.ReadFile(metaPath)

codegen/internal/generator/model.go

@@ -571,7 +571,7 @@ func buildSchemas(doc *v3.Document, params Params, resolver *typeResolver) []sch
 	result := make([]schemaModel, 0, len(names))
 	for _, name := range names {
 		ref := doc.Components.Schemas.GetOrZero(name)
-		if ref == nil {
+		if ref == nil || isPlainScalarSchema(ref.Schema()) {
 			continue
 		}
 		description := schemaDescription(ref)
@@ -617,7 +617,7 @@ func buildSchemas(doc *v3.Document, params Params, resolver *typeResolver) []sch
 }
 
 // shouldGenerateBuilder reports whether the model should expose a builder.
-// Single-field wrapper records (for example Lon/Lat/Meta-style aliases) don't
+// Single-field wrapper records (for example map aliases) don't
 // benefit from a builder and should use the canonical record constructor.
 func shouldGenerateBuilder(fields []schemaField, additionalProps *additionalPropertiesModel) bool {
 	if additionalProps != nil {

codegen/internal/generator/render.go

@@ -90,9 +90,6 @@ func renderSumUpClient(model sdkModel, params Params) error {
 
 // renderModels generates POJO classes that mirror OpenAPI schemas.
 func renderModels(model sdkModel, params Params) error {
-	if len(model.Schemas) == 0 {
-		return nil
-	}
 	dir := filepath.Join(params.OutputDir, params.modelPackagePath())
 	if err := os.RemoveAll(dir); err != nil {
 		return fmt.Errorf("remove models directory: %w", err)

codegen/internal/generator/scalars_test.go

@@ -0,0 +1,115 @@
+package generator
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+func TestGenerateScalarReferences(t *testing.T) {
+	t.Parallel()
+
+	tmp := t.TempDir()
+	specPath := filepath.Join(tmp, "openapi.yaml")
+	spec := `openapi: 3.1.0
+info: {title: Scalars, version: '1'}
+paths:
+  /readers/{id}:
+    post:
+      operationId: createReader
+      x-codegen: {method_name: create}
+      tags: [Readers]
+      parameters:
+        - name: id
+          in: path
+          required: true
+          schema: {$ref: '#/components/schemas/Name'}
+      requestBody:
+        required: true
+        content:
+          application/json:
+            schema: {$ref: '#/components/schemas/Request'}
+      responses:
+        '200':
+          description: Name
+          content:
+            application/json:
+              schema: {$ref: '#/components/schemas/Name'}
+components:
+  schemas:
+    Name: {type: string, description: Reader display name., example: Counter 1}
+    Count: {type: integer, format: int32}
+    Total: {type: integer, format: int64}
+    Latitude: {type: number, format: float}
+    Amount: {type: number, format: double}
+    Enabled: {type: boolean}
+    Date: {type: string, format: date}
+    Timestamp: {type: string, format: date-time}
+    Identifier: {type: string, format: uuid}
+    NullableName: {type: [string, 'null']}
+    Status: {type: string, enum: [active, inactive]}
+    Request:
+      type: object
+      required: [name, nullableName]
+      properties:
+        name: {$ref: '#/components/schemas/Name'}
+        nullableName: {$ref: '#/components/schemas/NullableName'}
+        count: {$ref: '#/components/schemas/Count'}
+        total: {$ref: '#/components/schemas/Total'}
+        latitude: {$ref: '#/components/schemas/Latitude'}
+        amount: {$ref: '#/components/schemas/Amount'}
+        enabled: {$ref: '#/components/schemas/Enabled'}
+        date: {$ref: '#/components/schemas/Date'}
+        timestamp: {$ref: '#/components/schemas/Timestamp'}
+        identifier: {$ref: '#/components/schemas/Identifier'}
+        status: {$ref: '#/components/schemas/Status'}
+        names:
+          type: array
+          items: {$ref: '#/components/schemas/Name'}
+        counts:
+          type: object
+          additionalProperties: {$ref: '#/components/schemas/Count'}
+`
+	if err := os.WriteFile(specPath, []byte(spec), 0o600); err != nil {
+		t.Fatal(err)
+	}
+	params := Params{SpecPath: specPath, OutputDir: filepath.Join(tmp, "java"), ResourceDir: filepath.Join(tmp, "resources")}
+	if err := Run(t.Context(), params); err != nil {
+		t.Fatal(err)
+	}
+	read := func(path string) string {
+		t.Helper()
+		data, err := os.ReadFile(filepath.Join(params.OutputDir, "com/sumup/sdk", path))
+		if err != nil {
+			t.Fatal(err)
+		}
+		return string(data)
+	}
+	request := read("models/Request.java")
+	for _, field := range []string{
+		"String name", "String nullableName", "Integer count", "Long total", "Float latitude", "Double amount",
+		"Boolean enabled", "java.time.LocalDate date", "java.time.OffsetDateTime timestamp", "java.util.UUID identifier",
+		"com.sumup.sdk.models.Status status", "java.util.List<String> names", "java.util.Map<String, Integer> counts",
+		"Reader display name.", `Objects.requireNonNull(name, "name")`,
+	} {
+		assertContains(t, request, field)
+	}
+	assertNotContains(t, request, `Objects.requireNonNull(nullableName`)
+	for _, name := range []string{"Name", "NullableName", "Count", "Total", "Latitude", "Amount", "Enabled", "Date", "Timestamp", "Identifier"} {
+		assertFileDoesNotExist(t, filepath.Join(params.OutputDir, "com/sumup/sdk/models", name+".java"))
+	}
+	assertContains(t, read("models/Status.java"), "public static final Status ACTIVE")
+	assertContains(t, read("clients/ReadersClient.java"), "public String create(")
+	assertContains(t, read("clients/ReadersClient.java"), "String id")
+	assertContains(t, read("clients/ReadersAsyncClient.java"), "CompletableFuture<String> create(")
+
+	catalog, err := BuildSamples(params, "test")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(catalog.Samples) != 1 {
+		t.Fatalf("expected one sample, got %d", len(catalog.Samples))
+	}
+	assertContains(t, catalog.Samples[0].Source, `.name("Counter 1")`)
+	assertNotContains(t, catalog.Samples[0].Source, "new com.sumup.sdk.models.Name")
+}

codegen/internal/generator/types.go

@@ -40,7 +40,10 @@ func newTypeResolver(doc *v3.Document, params Params) *typeResolver {
 		inlineNameUsage: make(map[string]int),
 	}
 	if doc.Components != nil && doc.Components.Schemas != nil && doc.Components.Schemas.Len() > 0 {
-		for name := range doc.Components.Schemas.KeysFromOldest() {
+		for name, ref := range doc.Components.Schemas.FromOldest() {
+			if isPlainScalarSchema(schemaFromProxy(ref)) {
+				continue
+			}
 			className := pascalCase(name, "")
 			resolver.schemaTypes[name] = params.modelPackage() + "." + className
 			resolver.inlineNameUsage[className]++
@@ -76,7 +79,7 @@ func (r *typeResolver) javaType(ref *base.SchemaProxy, context ...string) javaTy
 	if ref == nil {
 		return r.genericMap()
 	}
-	if ref.IsReference() {
+	if ref.IsReference() && !isPlainScalarSchema(ref.Schema()) {
 		name := componentNameFromRef(ref.GetReference())
 		if name != "" {
 			fqn := r.schemaClassName(name)
@@ -172,6 +175,28 @@ func (r *typeResolver) parameterJavaType(ref *base.SchemaProxy, context ...strin
 	return r.javaType(ref, context...)
 }
 
+// isPlainScalarSchema identifies schemas that use Java's scalar types even when
+// named as components. Enums and composed schemas retain their model handling.
+func isPlainScalarSchema(schema *base.Schema) bool {
+	if schema == nil || len(schema.Enum) > 0 || len(schema.AllOf) > 0 || len(schema.OneOf) > 0 || len(schema.AnyOf) > 0 {
+		return false
+	}
+	scalar := false
+	for _, kind := range schema.Type {
+		switch kind {
+		case "string", "integer", "number", "boolean":
+			if scalar {
+				return false
+			}
+			scalar = true
+		case "null":
+		default:
+			return false
+		}
+	}
+	return scalar
+}
+
 // objectType handles schemas that look like objects by either emitting inline
 // models or falling back to generic map types.
 func (r *typeResolver) objectType(schema *base.Schema, context []string) javaType {
@@ -330,7 +355,7 @@ func (r *typeResolver) inlineSchemaModels(params Params) []schemaModel {
 				imports := sortedImports(map[string]struct{}{
 					"com.fasterxml.jackson.annotation.JsonCreator": {},
 					"com.fasterxml.jackson.annotation.JsonValue":   {},
-					"java.util.Objects":                           {},
+					"java.util.Objects":                            {},
 				})
 				models = append(models, schemaModel{
 					Name:             info.className,

examples/card-reader-checkout/src/main/java/com/sumup/examples/cardreader/CardReaderCheckoutExample.java

@@ -18,9 +18,7 @@ public static void main(String[] args) {
     SumUpClient client = new SumUpClient();
 
     Optional<String> readerId =
-        client.readers().list(merchantCode).items().stream()
-            .findFirst()
-            .map(reader -> reader.id().value());
+        client.readers().list(merchantCode).items().stream().findFirst().map(reader -> reader.id());
     if (readerId.isEmpty()) {
       System.err.println("Merchant has no paired readers.");
       return;

src/main/java/com/sumup/sdk/clients/MembershipsAsyncClient.java

@@ -110,7 +110,7 @@ public static final class ListMembershipsQueryParams {
      * @param value Filter memberships by resource kind.
      * @return This ListMembershipsQueryParams instance.
      */
-    public ListMembershipsQueryParams kind(com.sumup.sdk.models.ResourceType value) {
+    public ListMembershipsQueryParams kind(String value) {
       this.values.put("kind", Objects.requireNonNull(value, "kind"));
       return this;
     }
@@ -193,7 +193,7 @@ public ListMembershipsQueryParams resourceParentType(java.util.Map<String, Objec
      * @param value Filter memberships by resource kind.
      * @return This ListMembershipsQueryParams instance.
      */
-    public ListMembershipsQueryParams resourceType(com.sumup.sdk.models.ResourceType value) {
+    public ListMembershipsQueryParams resourceType(String value) {
       this.values.put("resource.type", Objects.requireNonNull(value, "resourceType"));
       return this;
     }

src/main/java/com/sumup/sdk/clients/MembershipsClient.java

@@ -105,7 +105,7 @@ public static final class ListMembershipsQueryParams {
      * @param value Filter memberships by resource kind.
      * @return This ListMembershipsQueryParams instance.
      */
-    public ListMembershipsQueryParams kind(com.sumup.sdk.models.ResourceType value) {
+    public ListMembershipsQueryParams kind(String value) {
       this.values.put("kind", Objects.requireNonNull(value, "kind"));
       return this;
     }
@@ -188,7 +188,7 @@ public ListMembershipsQueryParams resourceParentType(java.util.Map<String, Objec
      * @param value Filter memberships by resource kind.
      * @return This ListMembershipsQueryParams instance.
      */
-    public ListMembershipsQueryParams resourceType(com.sumup.sdk.models.ResourceType value) {
+    public ListMembershipsQueryParams resourceType(String value) {
       this.values.put("resource.type", Objects.requireNonNull(value, "resourceType"));
       return this;
     }

src/main/java/com/sumup/sdk/clients/ReadersAsyncClient.java

@@ -178,9 +178,7 @@ public CompletableFuture<com.sumup.sdk.models.CreateReaderCheckoutResponse> crea
    * @throws ApiException if the SumUp API returns an error.
    */
   public CompletableFuture<com.sumup.sdk.models.ReaderPaymentResponse> createGoCheckout(
-      String merchantCode,
-      com.sumup.sdk.models.ReaderId readerId,
-      com.sumup.sdk.models.ReaderPaymentRequestParams request)
+      String merchantCode, String readerId, com.sumup.sdk.models.ReaderPaymentRequestParams request)
       throws ApiException {
     return createGoCheckout(merchantCode, readerId, request, null);
   }
@@ -205,7 +203,7 @@ public CompletableFuture<com.sumup.sdk.models.ReaderPaymentResponse> createGoChe
    */
   public CompletableFuture<com.sumup.sdk.models.ReaderPaymentResponse> createGoCheckout(
       String merchantCode,
-      com.sumup.sdk.models.ReaderId readerId,
+      String readerId,
       com.sumup.sdk.models.ReaderPaymentRequestParams request,
       RequestOptions requestOptions)
       throws ApiException {
@@ -242,8 +240,7 @@ public CompletableFuture<com.sumup.sdk.models.ReaderPaymentResponse> createGoChe
    * @return CompletableFuture completed when the request finishes.
    * @throws ApiException if the SumUp API returns an error.
    */
-  public CompletableFuture<Void> delete(String merchantCode, com.sumup.sdk.models.ReaderId readerId)
-      throws ApiException {
+  public CompletableFuture<Void> delete(String merchantCode, String readerId) throws ApiException {
     return delete(merchantCode, readerId, null);
   }
 
@@ -262,8 +259,7 @@ public CompletableFuture<Void> delete(String merchantCode, com.sumup.sdk.models.
    * @throws ApiException if the SumUp API returns an error.
    */
   public CompletableFuture<Void> delete(
-      String merchantCode, com.sumup.sdk.models.ReaderId readerId, RequestOptions requestOptions)
-      throws ApiException {
+      String merchantCode, String readerId, RequestOptions requestOptions) throws ApiException {
     Objects.requireNonNull(merchantCode, "merchantCode");
     Objects.requireNonNull(readerId, "readerId");
     String path = "/v0.1/merchants/{merchant_code}/readers/{reader_id}";
@@ -290,8 +286,8 @@ public CompletableFuture<Void> delete(
    * @return CompletableFuture resolved with com.sumup.sdk.models.Reader parsed response.
    * @throws ApiException if the SumUp API returns an error.
    */
-  public CompletableFuture<com.sumup.sdk.models.Reader> get(
-      String merchantCode, com.sumup.sdk.models.ReaderId readerId) throws ApiException {
+  public CompletableFuture<com.sumup.sdk.models.Reader> get(String merchantCode, String readerId)
+      throws ApiException {
     return get(merchantCode, readerId, null);
   }
 
@@ -311,8 +307,7 @@ public CompletableFuture<com.sumup.sdk.models.Reader> get(
    * @throws ApiException if the SumUp API returns an error.
    */
   public CompletableFuture<com.sumup.sdk.models.Reader> get(
-      String merchantCode, com.sumup.sdk.models.ReaderId readerId, GetReaderHeaders getReader)
-      throws ApiException {
+      String merchantCode, String readerId, GetReaderHeaders getReader) throws ApiException {
     return get(merchantCode, readerId, getReader, null);
   }
 
@@ -333,7 +328,7 @@ public CompletableFuture<com.sumup.sdk.models.Reader> get(
    */
   public CompletableFuture<com.sumup.sdk.models.Reader> get(
       String merchantCode,
-      com.sumup.sdk.models.ReaderId readerId,
+      String readerId,
       GetReaderHeaders getReader,
       RequestOptions requestOptions)
       throws ApiException {
@@ -623,9 +618,7 @@ public CompletableFuture<Void> terminateCheckout(
    * @throws ApiException if the SumUp API returns an error.
    */
   public CompletableFuture<com.sumup.sdk.models.Reader> update(
-      String merchantCode,
-      com.sumup.sdk.models.ReaderId readerId,
-      com.sumup.sdk.models.UpdateReaderRequest request)
+      String merchantCode, String readerId, com.sumup.sdk.models.UpdateReaderRequest request)
       throws ApiException {
     return update(merchantCode, readerId, request, null);
   }
@@ -647,7 +640,7 @@ public CompletableFuture<com.sumup.sdk.models.Reader> update(
    */
   public CompletableFuture<com.sumup.sdk.models.Reader> update(
       String merchantCode,
-      com.sumup.sdk.models.ReaderId readerId,
+      String readerId,
       com.sumup.sdk.models.UpdateReaderRequest request,
       RequestOptions requestOptions)
       throws ApiException {