Add top-level saving/loading support for Records

Records can now be saved and loaded directly using one of the several
methods available.

Also, the TypeSerializer has been refactored.

configlib-core/src/main/java/de/exlll/configlib/ConfigurationProperties.java

@@ -1,7 +1,10 @@
 package de.exlll.configlib;
 
 import java.lang.reflect.Type;
-import java.util.*;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.LinkedHashMap;
+import java.util.Map;
 import java.util.function.Predicate;
 
 import static de.exlll.configlib.Validator.requireNonNull;

configlib-core/src/main/java/de/exlll/configlib/ConfigurationSerializer.java

@@ -1,52 +1,34 @@
 package de.exlll.configlib;
 
+import de.exlll.configlib.TypeComponent.ConfigurationField;
+
 import java.lang.reflect.Field;
-import java.util.LinkedHashMap;
-import java.util.List;
 import java.util.Map;
 
-final class ConfigurationSerializer<T> extends TypeSerializer<T, Field> {
+final class ConfigurationSerializer<T> extends TypeSerializer<T, ConfigurationField> {
     ConfigurationSerializer(Class<T> configurationType, ConfigurationProperties properties) {
         super(Validator.requireConfiguration(configurationType), properties);
     }
 
-    @Override
-    public Map<?, ?> serialize(T element) {
-        final Map<String, Object> result = new LinkedHashMap<>();
-
-        for (final Field field : filterFields()) {
-            final Object fieldValue = Reflect.getValue(field, element);
-
-            if ((fieldValue == null) && !properties.outputNulls())
-                continue;
-
-            final Object serializedValue = serialize(field.getName(), fieldValue);
-
-            final String formattedField = properties.getNameFormatter().format(field.getName());
-            result.put(formattedField, serializedValue);
-        }
-
-        return result;
-    }
-
     @Override
     public T deserialize(Map<?, ?> element) {
         final T result = Reflect.newInstance(type);
 
-        for (final Field field : filterFields()) {
+        for (final var component : components()) {
-            final String fieldFormatted = properties.getNameFormatter().format(field.getName());
+            final var formattedName = formatter.format(component.componentName());
 
-            if (!element.containsKey(fieldFormatted))
+            if (!element.containsKey(formattedName))
                 continue;
 
-            final Object serializedValue = element.get(fieldFormatted);
+            final var serializedValue = element.get(formattedName);
+            final var field = component.component();
 
-            if (serializedValue == null && properties.inputNulls()) {
+            if ((serializedValue == null) && properties.inputNulls()) {
                 requireNonPrimitiveFieldType(field);
                 Reflect.setValue(field, result, null);
             } else if (serializedValue != null) {
-                final Object deserialized = deserialize(field, field.getName(), serializedValue);
+                Object deserializeValue = deserialize(component, serializedValue);
-                Reflect.setValue(field, result, deserialized);
+                Reflect.setValue(field, result, deserializeValue);
             }
         }
 
@@ -54,7 +36,7 @@ final class ConfigurationSerializer<T> extends TypeSerializer<T, Field> {
     }
 
     @Override
-    protected void requireSerializableParts() {
+    protected void requireSerializableComponents() {
         if (serializers.isEmpty()) {
             String msg = "Configuration class '" + type.getSimpleName() + "' " +
                          "does not contain any (de-)serializable fields.";
@@ -63,9 +45,22 @@ final class ConfigurationSerializer<T> extends TypeSerializer<T, Field> {
     }
 
     @Override
-    protected String baseDeserializeExceptionMessage(Field field, Object value) {
+    protected String baseDeserializeExceptionMessage(ConfigurationField component, Object value) {
         return "Deserialization of value '%s' with type '%s' for field '%s' failed."
-                .formatted(value, value.getClass(), field);
+                .formatted(value, value.getClass(), component.component());
+    }
+
+    @Override
+    protected Iterable<ConfigurationField> components() {
+        return FieldExtractors.CONFIGURATION.extract(type)
+                .filter(properties.getFieldFilter())
+                .map(ConfigurationField::new)
+                .toList();
+    }
+
+    @Override
+    T newDefaultInstance() {
+        return Reflect.newInstance(type);
     }
 
     private static void requireNonPrimitiveFieldType(Field field) {
@@ -76,12 +71,6 @@ final class ConfigurationSerializer<T> extends TypeSerializer<T, Field> {
         }
     }
 
-    private List<Field> filterFields() {
-        return FieldExtractors.CONFIGURATION.extract(type)
-                .filter(properties.getFieldFilter())
-                .toList();
-    }
-
     Class<T> getConfigurationType() {
         return type;
     }

configlib-core/src/main/java/de/exlll/configlib/RecordSerializer.java

@@ -1,61 +1,42 @@
 package de.exlll.configlib;
 
+import de.exlll.configlib.TypeComponent.ConfigurationRecordComponent;
+
 import java.lang.reflect.RecordComponent;
-import java.util.LinkedHashMap;
+import java.util.Arrays;
+import java.util.List;
 import java.util.Map;
 
-final class RecordSerializer<R extends Record> extends TypeSerializer<R, RecordComponent> {
+final class RecordSerializer<R> extends
+        TypeSerializer<R, ConfigurationRecordComponent> {
     RecordSerializer(Class<R> recordType, ConfigurationProperties properties) {
         super(Validator.requireRecord(recordType), properties);
     }
 
-    @Override
-    public Map<?, ?> serialize(R element) {
-        final Map<String, Object> result = new LinkedHashMap<>();
-
-        for (final RecordComponent component : type.getRecordComponents()) {
-            final Object componentValue = Reflect.getValue(component, element);
-
-            if (componentValue == null && !properties.outputNulls())
-                continue;
-
-            final Object resultValue = serialize(component.getName(), componentValue);
-
-            final String compName = properties.getNameFormatter().format(component.getName());
-            result.put(compName, resultValue);
-        }
-
-        return result;
-    }
-
     @Override
     public R deserialize(Map<?, ?> element) {
-        final var components = type.getRecordComponents();
+        final var components = components();
-        final var constructorArguments = new Object[components.length];
+        final var constructorArguments = new Object[components.size()];
 
-        for (int i = 0; i < components.length; i++) {
+        for (int i = 0, size = components.size(); i < size; i++) {
-            final var component = components[i];
+            final var component = components.get(i);
-            final var componentFormatted = properties.getNameFormatter()
+            final var formattedName = formatter.format(component.componentName());
-                    .format(component.getName());
 
-            if (!element.containsKey(componentFormatted)) {
+            if (!element.containsKey(formattedName)) {
-                constructorArguments[i] = Reflect.getDefaultValue(component.getType());
+                constructorArguments[i] = Reflect.getDefaultValue(component.componentType());
                 continue;
             }
 
-            final Object serializedArgument = element.get(componentFormatted);
+            final var serializedValue = element.get(formattedName);
+            final var recordComponent = component.component();
 
-            if (serializedArgument == null && properties.inputNulls()) {
+            if ((serializedValue == null) && properties.inputNulls()) {
-                requireNonPrimitiveComponentType(component);
+                requireNonPrimitiveComponentType(recordComponent);
                 constructorArguments[i] = null;
-            } else if (serializedArgument == null) {
+            } else if (serializedValue == null) {
-                constructorArguments[i] = Reflect.getDefaultValue(component.getType());
+                constructorArguments[i] = Reflect.getDefaultValue(component.componentType());
             } else {
-                constructorArguments[i] = deserialize(
+                constructorArguments[i] = deserialize(component, serializedValue);
-                        component,
-                        component.getName(),
-                        serializedArgument
-                );
             }
         }
 
@@ -63,7 +44,7 @@ final class RecordSerializer<R extends Record> extends TypeSerializer<R, RecordC
     }
 
     @Override
-    protected void requireSerializableParts() {
+    protected void requireSerializableComponents() {
         if (serializers.isEmpty()) {
             String msg = "Record type '%s' does not define any components."
                     .formatted(type.getSimpleName());
@@ -72,9 +53,21 @@ final class RecordSerializer<R extends Record> extends TypeSerializer<R, RecordC
     }
 
     @Override
-    protected String baseDeserializeExceptionMessage(RecordComponent component, Object value) {
+    protected String baseDeserializeExceptionMessage(ConfigurationRecordComponent component, Object value) {
         return "Deserialization of value '%s' with type '%s' for component '%s' of record '%s' failed."
-                .formatted(value, value.getClass(), component, component.getDeclaringRecord());
+                .formatted(value, value.getClass(), component.component(), component.declaringType());
+    }
+
+    @Override
+    protected List<ConfigurationRecordComponent> components() {
+        return Arrays.stream(type.getRecordComponents())
+                .map(ConfigurationRecordComponent::new)
+                .toList();
+    }
+
+    @Override
+    R newDefaultInstance() {
+        return Reflect.newRecordDefaultValues(type);
     }
 
     private static void requireNonPrimitiveComponentType(RecordComponent component) {

configlib-core/src/main/java/de/exlll/configlib/Reflect.java

@@ -8,6 +8,8 @@ import java.util.Set;
 import java.util.stream.Collectors;
 import java.util.stream.Stream;
 
+import static de.exlll.configlib.Validator.requireRecord;
+
 final class Reflect {
     private static final Map<Class<?>, Object> DEFAULT_VALUES = initDefaultValues();
 
@@ -60,9 +62,11 @@ final class Reflect {
         }
     }
 
-    static <R extends Record> R newRecord(Class<R> recordType, Object... constructorArguments) {
+    // We could use <R extends Record> as a bound here and for the other methods below
+    // but that would require casts elsewhere.
+    static <R> R newRecord(Class<R> recordType, Object... constructorArguments) {
         try {
-            Constructor<R> constructor = getCanonicalConstructor(recordType);
+            Constructor<R> constructor = getCanonicalConstructor(requireRecord(recordType));
             constructor.setAccessible(true);
             return constructor.newInstance(constructorArguments);
         } catch (NoSuchMethodException e) {
@@ -81,12 +85,23 @@ final class Reflect {
         }
     }
 
-    static <R extends Record> Constructor<R> getCanonicalConstructor(Class<R> recordType)
+    static <R> R newRecordDefaultValues(Class<R> recordType) {
+        final Object[] args = Arrays.stream(recordParameterTypes(requireRecord(recordType)))
+                .map(Reflect::getDefaultValue)
+                .toArray(Object[]::new);
+        return Reflect.newRecord(recordType, args);
+    }
+
+    static <R> Constructor<R> getCanonicalConstructor(Class<R> recordType)
             throws NoSuchMethodException {
-        Class<?>[] parameterTypes = Arrays.stream(recordType.getRecordComponents())
+        Class<?>[] parameterTypes = recordParameterTypes(requireRecord(recordType));
+        return recordType.getDeclaredConstructor(parameterTypes);
+    }
+
+    private static <R> Class<?>[] recordParameterTypes(Class<R> recordType) {
+        return Arrays.stream(recordType.getRecordComponents())
                 .map(RecordComponent::getType)
                 .toArray(Class<?>[]::new);
-        return recordType.getDeclaredConstructor(parameterTypes);
     }
 
     static <T> T[] newArray(Class<T> componentType, int length) {

configlib-core/src/main/java/de/exlll/configlib/TypeComponent.java

@@ -43,6 +43,12 @@ sealed interface TypeComponent<T> {
      */
     Object componentValue(Object componentHolder);
 
+    /**
+     * Returns the type that declares this component.
+     *
+     * @return the declaring type
+     */
+    Class<?> declaringType();
 
     record ConfigurationField(Field component) implements TypeComponent<Field> {
         public ConfigurationField(Field component) {
@@ -63,6 +69,11 @@ sealed interface TypeComponent<T> {
         public Object componentValue(Object componentHolder) {
             return Reflect.getValue(component, componentHolder);
         }
+
+        @Override
+        public Class<?> declaringType() {
+            return component.getDeclaringClass();
+        }
     }
 
     record ConfigurationRecordComponent(RecordComponent component)
@@ -85,6 +96,11 @@ sealed interface TypeComponent<T> {
         public Object componentValue(Object componentHolder) {
             return Reflect.getValue(component, componentHolder);
         }
+
+        @Override
+        public Class<?> declaringType() {
+            return component.getDeclaringRecord();
+        }
     }
 }
 

configlib-core/src/main/java/de/exlll/configlib/TypeSerializer.java

@@ -1,51 +1,89 @@
 package de.exlll.configlib;
 
+import java.util.LinkedHashMap;
 import java.util.Map;
 
 import static de.exlll.configlib.Validator.requireNonNull;
 
-abstract class TypeSerializer<T, P> implements Serializer<T, Map<?, ?>> {
+sealed abstract class TypeSerializer<T, TC extends TypeComponent<?>>
+        implements Serializer<T, Map<?, ?>>
+        permits ConfigurationSerializer, RecordSerializer {
     protected final Class<T> type;
     protected final ConfigurationProperties properties;
+    protected final NameFormatter formatter;
     protected final Map<String, Serializer<?, ?>> serializers;
 
     protected TypeSerializer(Class<T> type, ConfigurationProperties properties) {
         this.type = requireNonNull(type, "type");
         this.properties = requireNonNull(properties, "configuration properties");
+        this.formatter = properties.getNameFormatter();
         this.serializers = new SerializerMapper(type, properties).buildSerializerMap();
-        requireSerializableParts();
+        requireSerializableComponents();
     }
 
-    protected final Object serialize(String partName, Object value) {
+    static <T> TypeSerializer<T, ?> newSerializerFor(
+            Class<T> type,
+            ConfigurationProperties properties
+    ) {
+        return type.isRecord()
+                ? new RecordSerializer<>(type, properties)
+                : new ConfigurationSerializer<>(type, properties);
+    }
+
+    @Override
+    public final Map<?, ?> serialize(T element) {
+        final Map<String, Object> result = new LinkedHashMap<>();
+
+        for (final TC component : components()) {
+            final Object componentValue = component.componentValue(element);
+
+            if ((componentValue == null) && !properties.outputNulls())
+                continue;
+
+            final Object serializedValue = serialize(component, componentValue);
+            final String formattedName = formatter.format(component.componentName());
+            result.put(formattedName, serializedValue);
+        }
+
+        return result;
+    }
+
+    protected final Object serialize(TC component, Object value) {
         // The following cast won't cause a ClassCastException because the serializers
-        // are selected based on the part type.
+        // are selected based on the component type.
         @SuppressWarnings("unchecked")
-        final var serializer = (Serializer<Object, Object>) serializers.get(partName);
+        final var serializer = (Serializer<Object, Object>)
+                serializers.get(component.componentName());
         return (value != null) ? serializer.serialize(value) : null;
     }
 
-    protected final Object deserialize(P part, String partName, Object value) {
+    protected final Object deserialize(TC component, Object value) {
         // This unchecked cast leads to an exception if the type of the object which
         // is deserialized is not a subtype of the type the deserializer expects.
         @SuppressWarnings("unchecked")
-        final var serializer = (Serializer<Object, Object>) serializers.get(partName);
+        final var serializer = (Serializer<Object, Object>)
+                serializers.get(component.componentName());
 
         final Object deserialized;
         try {
             deserialized = serializer.deserialize(value);
         } catch (ClassCastException e) {
-            String msg = baseDeserializeExceptionMessage(part, value) + "\n" +
+            String msg = baseDeserializeExceptionMessage(component, value) + "\n" +
                          "The type of the object to be deserialized does not " +
                          "match the type the deserializer expects.";
             throw new ConfigurationException(msg, e);
         } catch (RuntimeException e) {
-            String msg = baseDeserializeExceptionMessage(part, value);
+            String msg = baseDeserializeExceptionMessage(component, value);
             throw new ConfigurationException(msg, e);
         }
         return deserialized;
     }
 
-    protected abstract void requireSerializableParts();
+    protected abstract void requireSerializableComponents();
+
+    protected abstract String baseDeserializeExceptionMessage(TC component, Object value);
+
+    protected abstract Iterable<TC> components();
 
-    protected abstract String baseDeserializeExceptionMessage(P part, Object value);
+    abstract T newDefaultInstance();
 }

configlib-core/src/main/java/de/exlll/configlib/YamlConfigurationStore.java

@@ -31,7 +31,7 @@ public final class YamlConfigurationStore<T> implements FileConfigurationStore<T
     private static final Load YAML_LOADER = newYamlLoader();
     private final Class<T> configurationType;
     private final YamlConfigurationProperties properties;
-    private final ConfigurationSerializer<T> serializer;
+    private final TypeSerializer<T, ?> serializer;
     private final CommentNodeExtractor extractor;
 
     /**
@@ -44,7 +44,7 @@ public final class YamlConfigurationStore<T> implements FileConfigurationStore<T
     public YamlConfigurationStore(Class<T> configurationType, YamlConfigurationProperties properties) {
         this.configurationType = requireNonNull(configurationType, "configuration type");
         this.properties = requireNonNull(properties, "properties");
-        this.serializer = new ConfigurationSerializer<>(configurationType, properties);
+        this.serializer = TypeSerializer.newSerializerFor(configurationType, properties);
         this.extractor = new CommentNodeExtractor(properties);
     }
 
@@ -83,7 +83,7 @@ public final class YamlConfigurationStore<T> implements FileConfigurationStore<T
     public T load(Path configurationFile) {
         try (var reader = Files.newBufferedReader(configurationFile)) {
             var yaml = YAML_LOADER.loadFromReader(reader);
-            var conf = requireConfiguration(yaml, configurationFile);
+            var conf = requireYamlMap(yaml, configurationFile);
             return serializer.deserialize(conf);
         } catch (YamlEngineException e) {
             String msg = "The configuration file at %s does not contain valid YAML.";
@@ -93,7 +93,7 @@ public final class YamlConfigurationStore<T> implements FileConfigurationStore<T
         }
     }
 
-    private Map<?, ?> requireConfiguration(Object yaml, Path configurationFile) {
+    private Map<?, ?> requireYamlMap(Object yaml, Path configurationFile) {
         if (yaml == null) {
             String msg = "The configuration file at %s is empty or only contains null.";
             throw new ConfigurationException(msg.formatted(configurationFile));
@@ -116,7 +116,7 @@ public final class YamlConfigurationStore<T> implements FileConfigurationStore<T
             save(configuration, configurationFile);
             return configuration;
         }
-        T configuration = Reflect.newInstance(configurationType);
+        T configuration = serializer.newDefaultInstance();
         save(configuration, configurationFile);
         return configuration;
     }

configlib-core/src/test/java/de/exlll/configlib/ReflectTest.java

@@ -10,10 +10,10 @@ import java.util.ArrayList;
 import java.util.HashMap;
 import java.util.HashSet;
 
-import static de.exlll.configlib.TestUtils.assertThrowsRuntimeException;
+import static de.exlll.configlib.TestUtils.*;
-import static de.exlll.configlib.TestUtils.getField;
 import static org.hamcrest.MatcherAssert.assertThat;
 import static org.hamcrest.Matchers.*;
+import static org.junit.jupiter.api.Assertions.*;
 
 class ReflectTest {
 
@@ -305,4 +305,36 @@ class ReflectTest {
                 "The canonical constructor of record type 'R3' threw an exception."
         );
     }
+
+    @Test
+    void newRecordRequiresRecordType() {
+        class A {}
+        assertThrowsConfigurationException(
+                () -> Reflect.newRecord(A.class),
+                "Class 'A' must be a record."
+        );
+    }
+
+    @Test
+    void newRecordWithDefaultValues() {
+        record E() {}
+        record R(boolean a, char b, byte c, short d, int e, long f, float g, double h,
+                 Boolean i, Character j, Integer k, Float l, E m, R n, Object o) {}
+        R r = Reflect.newRecordDefaultValues(R.class);
+        assertFalse(r.a);
+        assertEquals('\0', r.b);
+        assertEquals(0, r.c);
+        assertEquals(0, r.d);
+        assertEquals(0, r.e);
+        assertEquals(0, r.f);
+        assertEquals(0, r.g);
+        assertEquals(0, r.h);
+        assertNull(r.i);
+        assertNull(r.j);
+        assertNull(r.k);
+        assertNull(r.l);
+        assertNull(r.m);
+        assertNull(r.n);
+        assertNull(r.o);
+    }
 }

configlib-core/src/test/java/de/exlll/configlib/TypeComponentTest.java

@@ -35,6 +35,11 @@ class TypeComponentTest {
         void componentValue() {
             assertThat(COMPONENT.componentValue(new C()), is(20));
         }
+
+        @Test
+        void declaringType() {
+            assertThat(COMPONENT.declaringType(), equalTo(C.class));
+        }
     }
 
     static final class ConfigurationRecordComponentTest {
@@ -58,5 +63,10 @@ class TypeComponentTest {
         void componentValue() {
             assertThat(COMPONENT.componentValue(new R(10f)), is(10f));
         }
+
+        @Test
+        void declaringType() {
+            assertThat(COMPONENT.declaringType(), equalTo(R.class));
+        }
     }
 }

configlib-core/src/test/java/de/exlll/configlib/YamlConfigurationPropertiesTest.java

@@ -4,7 +4,6 @@ import org.junit.jupiter.api.Test;
 
 import static org.hamcrest.MatcherAssert.assertThat;
 import static org.hamcrest.Matchers.is;
-import static org.junit.jupiter.api.Assertions.*;
 
 class YamlConfigurationPropertiesTest {
     @Test

configlib-core/src/test/java/de/exlll/configlib/YamlConfigurationStoreTest.java

@@ -61,6 +61,33 @@ class YamlConfigurationStoreTest {
         assertEquals(expected, TestUtils.readFile(yamlFile));
     }
 
+    @Test
+    void saveRecord() {
+        record R(String s, @Comment("A comment") Integer i) {}
+        YamlConfigurationProperties properties = YamlConfigurationProperties.newBuilder()
+                .header("The\nHeader")
+                .footer("The\nFooter")
+                .outputNulls(true)
+                .setNameFormatter(String::toUpperCase)
+                .build();
+        YamlConfigurationStore<R> store = new YamlConfigurationStore<>(R.class, properties);
+        store.save(new R("S1", null), yamlFile);
+
+        String expected =
+                """
+                # The
+                # Header
+                                
+                S: S1
+                # A comment
+                I: null
+                                
+                # The
+                # Footer\
+                """;
+        assertEquals(expected, TestUtils.readFile(yamlFile));
+    }
+
     @Configuration
     static final class B {
         String s = "S1";
@@ -97,6 +124,36 @@ class YamlConfigurationStoreTest {
         assertNull(config.i);
     }
 
+    @Test
+    void loadRecord() throws IOException {
+        record R(String s, String t, Integer i) {}
+        YamlConfigurationProperties properties = YamlConfigurationProperties.newBuilder()
+                .inputNulls(true)
+                .setNameFormatter(String::toUpperCase)
+                .build();
+        YamlConfigurationStore<R> store = new YamlConfigurationStore<>(R.class, properties);
+
+        Files.writeString(
+                yamlFile,
+                """
+                # The
+                # Header
+                                
+                S: S2
+                t: T2
+                I: null
+                                
+                # The
+                # Footer\
+                """
+        );
+
+        R config = store.load(yamlFile);
+        assertEquals("S2", config.s);
+        assertNull(config.t);
+        assertNull(config.i);
+    }
+
     @Configuration
     static final class C {
         int i;
@@ -207,6 +264,29 @@ class YamlConfigurationStoreTest {
         assertEquals(11, config.j);
     }
 
+    @Test
+    void updateCreatesConfigurationFileIfItDoesNotExistRecord() {
+        record R(int i, char c, String s) {}
+        YamlConfigurationStore<R> store = new YamlConfigurationStore<>(
+                R.class,
+                YamlConfigurationProperties.newBuilder().outputNulls(true).build()
+        );
+
+        assertFalse(Files.exists(yamlFile));
+        R config = store.update(yamlFile);
+        assertEquals(
+                """
+                i: 0
+                c: "\\0"
+                s: null\
+                """,
+                readFile(yamlFile)
+        );
+        assertEquals(0, config.i);
+        assertEquals('\0', config.c);
+        assertNull(config.s);
+    }
+
     @Test
     void updateLoadsConfigurationFileIfItDoesExist() throws IOException {
         YamlConfigurationStore<E> store = newDefaultStore(E.class);
@@ -217,6 +297,17 @@ class YamlConfigurationStoreTest {
         assertEquals(11, config.j);
     }
 
+    @Test
+    void updateLoadsConfigurationFileIfItDoesExistRecord() throws IOException {
+        record R(int i, int j) {}
+        YamlConfigurationStore<R> store = newDefaultStore(R.class);
+
+        Files.writeString(yamlFile, "i: 20");
+        R config = store.update(yamlFile);
+        assertEquals(20, config.i);
+        assertEquals(0, config.j);
+    }
+
     @Test
     void updateUpdatesFile() throws IOException {
         YamlConfigurationStore<E> store = newDefaultStore(E.class);
@@ -228,6 +319,18 @@ class YamlConfigurationStoreTest {
         assertEquals("i: 20\nj: 11", readFile(yamlFile));
     }
 
+    @Test
+    void updateUpdatesFileRecord() throws IOException {
+        record R(int i, int j) {}
+        YamlConfigurationStore<R> store = newDefaultStore(R.class);
+
+        Files.writeString(yamlFile, "i: 20\nk: 30");
+        R config = store.update(yamlFile);
+        assertEquals(20, config.i);
+        assertEquals(0, config.j);
+        assertEquals("i: 20\nj: 0", readFile(yamlFile));
+    }
+
     private static <T> YamlConfigurationStore<T> newDefaultStore(Class<T> configType) {
         YamlConfigurationProperties properties = YamlConfigurationProperties.newBuilder().build();
         return new YamlConfigurationStore<>(configType, properties);