DATAMONGO-743 - Added DBObjectToStringConverter.

Added a reading converter to dump DBObject instances into a String directly to enable executing queries against MongoDB into a String version of the query result without marshaling the DBObject into a Map first.

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/convert/CustomConversions.java

@@ -39,6 +39,7 @@ import org.springframework.data.convert.WritingConverter;
 import org.springframework.data.mapping.model.SimpleTypeHolder;
 import org.springframework.data.mongodb.core.convert.MongoConverters.BigDecimalToStringConverter;
 import org.springframework.data.mongodb.core.convert.MongoConverters.BigIntegerToStringConverter;
+import org.springframework.data.mongodb.core.convert.MongoConverters.DBObjectToStringConverter;
 import org.springframework.data.mongodb.core.convert.MongoConverters.StringToBigDecimalConverter;
 import org.springframework.data.mongodb.core.convert.MongoConverters.StringToBigIntegerConverter;
 import org.springframework.data.mongodb.core.convert.MongoConverters.StringToURLConverter;
@@ -98,6 +99,7 @@ public class CustomConversions {
 		this.converters.add(StringToBigIntegerConverter.INSTANCE);
 		this.converters.add(URLToStringConverter.INSTANCE);
 		this.converters.add(StringToURLConverter.INSTANCE);
+		this.converters.add(DBObjectToStringConverter.INSTANCE);
 		this.converters.addAll(JodaTimeConverters.getConvertersToRegister());
 		this.converters.addAll(converters);
 

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/convert/MongoConverters.java

@@ -24,8 +24,11 @@ import org.bson.types.ObjectId;
 import org.springframework.core.convert.ConversionFailedException;
 import org.springframework.core.convert.TypeDescriptor;
 import org.springframework.core.convert.converter.Converter;
+import org.springframework.data.convert.ReadingConverter;
 import org.springframework.util.StringUtils;
 
+import com.mongodb.DBObject;
+
 /**
  * Wrapper class to contain useful converters for the usage with Mongo.
  * 
@@ -147,4 +150,15 @@ abstract class MongoConverters {
 			}
 		}
 	}
+
+	@ReadingConverter
+	public static enum DBObjectToStringConverter implements Converter<DBObject, String> {
+
+		INSTANCE;
+
+		@Override
+		public String convert(DBObject source) {
+			return source == null ? null : source.toString();
+		}
+	}
 }

spring-data-mongodb/src/test/java/org/springframework/data/mongodb/core/convert/MappingMongoConverterUnitTests.java

@@ -1415,6 +1415,16 @@ public class MappingMongoConverterUnitTests {
 		assertThat(((Person) value).lastname, is("converter"));
 	}
 
+	/**
+	 * @see DATAMONGO-743
+	 */
+	@Test
+	public void readsIntoStringsOutOfTheBox() {
+
+		DBObject dbObject = new BasicDBObject("firstname", "Dave");
+		assertThat(converter.read(String.class, dbObject), is("{ \"firstname\" : \"Dave\"}"));
+	}
+
 	@Document
 	class MapDBRef {
 		@org.springframework.data.mongodb.core.mapping.DBRef Map<String, MapDBRefVal> map;