Add a property for Data MongoDB's BigDecimal representation

Closes gh-47041

module/spring-boot-data-mongodb/src/main/java/org/springframework/boot/data/mongodb/autoconfigure/DataMongoProperties.java

@@ -19,6 +19,7 @@ package org.springframework.boot.data.mongodb.autoconfigure;
 import org.jspecify.annotations.Nullable;
 
 import org.springframework.boot.context.properties.ConfigurationProperties;
+import org.springframework.data.mongodb.core.convert.MongoCustomConversions.BigDecimalRepresentation;
 
 /**
  * Configuration properties for Spring Data MongoDB.
@@ -41,6 +42,8 @@ public class DataMongoProperties {
 
 	private final Gridfs gridfs = new Gridfs();
 
+	private final Representation representation = new Representation();
+
 	public @Nullable Boolean isAutoIndexCreation() {
 		return this.autoIndexCreation;
 	}
@@ -61,6 +64,10 @@ public class DataMongoProperties {
 		return this.gridfs;
 	}
 
+	public Representation getRepresentation() {
+		return this.representation;
+	}
+
 	public static class Gridfs {
 
 		/**
@@ -91,4 +98,21 @@ public class DataMongoProperties {
 
 	}
 
+	public static class Representation {
+
+		/**
+		 * Representation to use when converting a BigDecimal.
+		 */
+		private BigDecimalRepresentation bigDecimal = BigDecimalRepresentation.DECIMAL128;
+
+		public BigDecimalRepresentation getBigDecimal() {
+			return this.bigDecimal;
+		}
+
+		public void setBigDecimal(BigDecimalRepresentation bigDecimal) {
+			this.bigDecimal = bigDecimal;
+		}
+
+	}
+
 }

module/spring-boot-data-mongodb/src/main/java/org/springframework/boot/data/mongodb/autoconfigure/MongoDataConfiguration.java

@@ -16,8 +16,6 @@
 
 package org.springframework.boot.data.mongodb.autoconfigure;
 
-import java.util.Collections;
-
 import org.springframework.beans.BeanUtils;
 import org.springframework.beans.factory.ObjectProvider;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;
@@ -48,6 +46,12 @@ import org.springframework.data.mongodb.core.mapping.MongoMappingContext;
 @Configuration(proxyBeanMethods = false)
 class MongoDataConfiguration {
 
+	private final DataMongoProperties properties;
+
+	MongoDataConfiguration(DataMongoProperties properties) {
+		this.properties = properties;
+	}
+
 	@Bean
 	@ConditionalOnMissingBean
 	static MongoManagedTypes mongoManagedTypes(ApplicationContext applicationContext) throws ClassNotFoundException {
@@ -56,13 +60,12 @@ class MongoDataConfiguration {
 
 	@Bean
 	@ConditionalOnMissingBean
-	MongoMappingContext mongoMappingContext(DataMongoProperties properties, MongoCustomConversions conversions,
-			MongoManagedTypes managedTypes) {
+	MongoMappingContext mongoMappingContext(MongoCustomConversions conversions, MongoManagedTypes managedTypes) {
 		PropertyMapper map = PropertyMapper.get().alwaysApplyingWhenNonNull();
 		MongoMappingContext context = new MongoMappingContext();
-		map.from(properties.isAutoIndexCreation()).to(context::setAutoIndexCreation);
+		map.from(this.properties.isAutoIndexCreation()).to(context::setAutoIndexCreation);
 		context.setManagedTypes(managedTypes);
-		Class<?> strategyClass = properties.getFieldNamingStrategy();
+		Class<?> strategyClass = this.properties.getFieldNamingStrategy();
 		if (strategyClass != null) {
 			context.setFieldNamingStrategy((FieldNamingStrategy) BeanUtils.instantiateClass(strategyClass));
 		}
@@ -73,7 +76,8 @@ class MongoDataConfiguration {
 	@Bean
 	@ConditionalOnMissingBean
 	MongoCustomConversions mongoCustomConversions() {
-		return new MongoCustomConversions(Collections.emptyList());
+		return MongoCustomConversions
+			.create((configurer) -> configurer.bigDecimal(this.properties.getRepresentation().getBigDecimal()));
 	}
 
 	@Bean

module/spring-boot-data-mongodb/src/test/java/org/springframework/boot/data/mongodb/autoconfigure/DataMongoPropertiesTests.java

@@ -20,6 +20,9 @@ import org.junit.jupiter.api.Test;
 
 import org.springframework.boot.autoconfigure.AutoConfigurations;
 import org.springframework.boot.test.context.runner.ApplicationContextRunner;
+import org.springframework.data.mongodb.core.convert.MongoCustomConversions.BigDecimalRepresentation;
+import org.springframework.data.mongodb.core.convert.MongoCustomConversions.MongoConverterConfigurationAdapter;
+import org.springframework.test.util.ReflectionTestUtils;
 
 import static org.assertj.core.api.Assertions.assertThat;
 
@@ -40,4 +43,16 @@ class DataMongoPropertiesTests {
 			});
 	}
 
+	@Test
+	void defaultBigDecimalRepresentationIsAlignedWithSpringData() {
+		BigDecimalRepresentation springDataDefault = springDataDefaultBigDecimalRepresentation();
+		BigDecimalRepresentation springBootDefault = new DataMongoProperties().getRepresentation().getBigDecimal();
+		assertThat(springBootDefault).isEqualTo(springDataDefault);
+	}
+
+	private BigDecimalRepresentation springDataDefaultBigDecimalRepresentation() {
+		return (BigDecimalRepresentation) ReflectionTestUtils.getField(new MongoConverterConfigurationAdapter(),
+				"bigDecimals");
+	}
+
 }

module/spring-boot-data-mongodb/src/test/java/org/springframework/boot/data/mongodb/autoconfigure/MongoDataAutoConfigurationTests.java

@@ -118,6 +118,26 @@ class MongoDataAutoConfigurationTests {
 		});
 	}
 
+	@Test
+	void customBigDecimalRepresentation() {
+		this.contextRunner.withPropertyValues("spring.data.mongodb.representation.big-decimal=string")
+			.run((context) -> assertThat(context.getBean(MongoCustomConversions.class)).extracting("converters")
+				.asInstanceOf(InstanceOfAssertFactories.LIST)
+				.map((converter) -> converter.getClass().getName())
+				.anySatisfy((className) -> assertThat(className).contains("BigDecimalToStringConverter"))
+				.anySatisfy((className) -> assertThat(className).contains("BigIntegerToStringConverter")));
+	}
+
+	@Test
+	void defaultBigDecimalRepresentation() {
+		this.contextRunner
+			.run((context) -> assertThat(context.getBean(MongoCustomConversions.class)).extracting("converters")
+				.asInstanceOf(InstanceOfAssertFactories.LIST)
+				.map((converter) -> converter.getClass().getName())
+				.noneSatisfy((className) -> assertThat(className).contains("BigDecimalToStringConverter"))
+				.noneSatisfy((className) -> assertThat(className).contains("BigIntegerToStringConverter")));
+	}
+
 	@Test
 	void usesAutoConfigurationPackageToPickUpDocumentTypes() {
 		AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext();