A presentation given at DevNation 2015 (Boston) of a prototype library that leverages Java Lambda Expressions to manage data on MongoDB.

1. Using Lambda
Expressions to Query a
Datastore
Xavier Coulon - Red Hat
@xcoulon

2. The idea

3. The idea
Lambda Expressions:
• provide type safety
• describe the "what", not the "how"

4. The idea

5. The idea
u -> ( u.firstName.equals("john") && u.lastName.equals("doe"))
|| u.userName.equals("jdoe"))
final List<User> users = userCollection.filter(
u -> ( u.firstName.equals("john") && u.lastName.equals("doe"))
|| u.userName.equals("jdoe")).toList();

6. Introducing project
Lambdamatic

7. Part I. The building blocks

8. Building blocks
• Metamodel generation
• Lambda Expression analysis

9. Metamodel generation
(à la JPA)

10. package com.example.domain;
public class User {
private String id;
private String firstName;
private String lastName;
private String userName;
}
Metamodel generation
package com.example.domain;
@Document(collection="users")
public class User {
@DocumentId
private String id;
@DocumentField
private String firstName;
private String lastName;
@DocumentField(name="uName")
private String userName;
}
package com.example.domain;
@Generated(value="LambdamaticAnnotationsProcessor")
public class QUser implements QueryMetadata<User> {
@DocumentField(name="_id")
public StringField firstName;
@DocumentField(name="firstName")
public StringField firstName;
@DocumentField(name="lastName")
public StringField lastName;
@DocumentField(name="uName")
public StringField userName;
}
Query Metadata class generation

11. Metamodel generation
package com.example.domain;
@Generated(value="o.l.m.a.DocumentAnnotationProcessor")
public class UserCollection extends
LambdamaticMongoCollectionImpl<User, QUser> {
public UserCollection(final MongoClient mongoClient,
final String databaseName) {
super(mongoClient, databaseName, "users", User.class);
}
}
Collection class
package com.example.domain;
@Document(collection="users")
public class User {
@DocumentId
private String id;
@DocumentField
private String firstName;
private String lastName;
@DocumentField(name="uName")
private String userName;
}

12. Metamodel generation
CDI Integration
@Generated(value="org.lambdamatic.mongodb.apt.DocumentAnnotationProcessor")
@ApplicationScoped
public class UserCollectionProducer {
@Produces
public UserCollection getUserCollection(final MongoClient mongoClient,
final MongoClientConfiguration mongoClientConfiguration) {
return new UserCollection(mongoClient, mongoClientConfiguration.getDatabaseName(), "users");
}
}

13. final List<User> users = userCollection.filter(
u -> ( u.firstName.equals("john") && u.lastName.equals("doe"))
|| u.userName.equals("jdoe")).toList();
Metamodel in action
public class UserCollection extends
LambdamaticMongoCollectionImpl<User, QUser> {
...
}
package com.example.domain;
@Generated(value="LambdamaticAnnotationsProcessor")
public class QUser implements QueryMetadata<User> {
@DocumentField(name="_id")
public StringField firstName;
@DocumentField(name="firstName")
public StringField firstName;
...
}

14. Metamodel benefits
Geospatial queries

15. Metamodel benefits
public class Location {
/** The latitude value.*/
private double latitude;
/** The longitude value.*/
private double longitude;
}
public List<BikeStation> findWithin(final Location[] corners) {
return bikeStationCollection.find(s -> s.location.geoWithin(corners))
.toList();
}
public class QBikeStation implements QueryMetadata<BikeStation> {
@DocumentField(name="location")
public LocationField location;
...
}
@Document(collection="bikestations")
public class BikeStation {
@DocumentField
private Location location;
...
}
public interface LocationField {
public boolean geoWithin(final Location[] corners);
...
}

16. Lambda Expression
Analysis
(this is the fun part, really)

17. Lambda Expression
Analysis

19. Lambda Expression
Analysis
@FunctionalInterface
public interface FilterExpression<T> extends Predicate<T>, Serializable { }
Step#1 : Use a Serializable Functional Interface

20. Lambda Expression
Analysis
public static <T> SerializedLambda getSerializedLambda(
final FilterExpression<T> expression) {
...
final Class<?> cl = expression.getClass();
final Method m = cl.getDeclaredMethod("writeReplace");
m.setAccessible(true);
return (SerializedLambda) m.invoke(expression);
...
}
Step#2 : Locate the generated method

21. Lambda Expression
Analysis
Step#3 : read the generated bytecode
Label L1125736023
VarInsn ALOAD #0
FieldInsn GETFIELD com/sample/QUser.firstName (desc=Lorg/lambdamatic/mongodb/metadata/StringField;)
LdcInsn john
MethodInsn INVOKEVIRTUAL java/lang/Object.equals (desc=(Ljava/lang/Object;)Z)
JumpInsn IFEQ L1636182655
VarInsn ALOAD #0
FieldInsn GETFIELD com/sample/QUser.lastName (desc=Lorg/lambdamatic/mongodb/metadata/StringField;)
Label L1122606666
LdcInsn doe
MethodInsn INVOKEVIRTUAL java/lang/Object.equals (desc=(Ljava/lang/Object;)Z)
JumpInsn IFNE L350068407
Label L1636182655
VarInsn ALOAD #0
FieldInsn GETFIELD com/sample/QUser.userName (desc=Lorg/lambdamatic/mongodb/metadata/StringField;)
LdcInsn jdoe
MethodInsn INVOKEVIRTUAL java/lang/Object.equals (desc=(Ljava/lang/Object;)Z)
JumpInsn IFNE L350068407
Insn ICONST_0
JumpInsn GOTO L1820383114
Label L350068407
Insn ICONST_1
Label L1820383114
Insn IRETURN
Label L369049246
LocalVariable u (desc=Lcom/sample/QUser;) index=0

22. Lambda Expression
Analysis
Step#4 : build an AST
if(u.firstName.equals("john")) {
if(u.lastName.equals("doe")) {
return true
} else {
if(u.userName.equals("jdoe")) {
return true
} else {
return false
}
}
} else {
if(u.userName.equals("jdoe")) {
return true
} else {
return false
}
}

23. if(u.firstName.equals("john")) {
if(u.lastName.equals("doe")) {
return true
} else {
if(u.userName.equals("jdoe")) {
return true
} else {
return false
}
}
} else {
if(u.userName.equals("jdoe")) {
return true
} else {
return false
}
}
if(u.firstName.equals("john")) {
if(u.lastName.equals("doe")) {
return true
} else {
if(u.userName.equals("jdoe")) {
return true
} else {
return false
}
}
} else {
if(u.userName.equals("jdoe")) {
return true
} else {
return false
}
(u.firstName.equals("john")
&& u.lastName.equals("doe"))
|| (u.firstName.equals("john")
&& !u.lastName.equals("doe")
&& u.userName.equals("jdoe"))
|| (!u.firstName.equals("john")
&& u.userName.equals("jdoe"))
Lambda Expression
Analysis
Step#5 : Thin out the AST

24. (u.firstName.equals("john")
&& u.lastName.equals("doe"))
|| (u.firstName.equals("john")
&& !u.lastName.equals("doe")
&& u.userName.equals("jdoe"))
|| (!u.firstName.equals("john")
&& u.userName.equals("jdoe"))
Lambda Expression
Analysis
Step#6 : Further simplify the AST
(u.firstName.equals("john")
&& u.lastName.equals("doe"))
|| (u.firstName.equals("john")
&& !u.lastName.equals("doe")
&& u.userName.equals("jdoe"))
|| (!u.firstName.equals("john")
&& u.userName.equals("jdoe"))

25. Lambda Expression
Analysis
Boolean algebra to the rescue !
a.(b.c) = a.b.c
a + (b + c) = a + b + c
a.(!a + b).(!a + c) = a.b.c
a + (!a.b) + (!a.c) = a + b + c
a.(a + b).(a + c) = a
a + (a.b) + (a.c) = a
(a.b) + (a.c) + (a.d) = a.(b + c + d)
(a + b).(a + c).(a + d) = a + (b.c.d)
a + a = a
a.a = a
a.!a = O
a + !a = I
O + a = a
O.a = O
1 + a = 1
1.a = a
a.(b + c + d) = (a.b) + (a.c) + (a.d)
a + (b.c.d) = (a + b).(a + c).(a + d)

27. Lambda Expression
Analysis
Step#6 : further simplify the statement tree
(u.firstName.equals("john")
&& u.lastName.equals("doe"))
|| (u.firstName.equals("john")
&& !u.lastName.equals("doe")
&& u.userName.equals("jdoe"))
|| (!u.firstName.equals("john")
&& u.userName.equals("jdoe"))
(u.firstName.equals("john") && u.lastName.equals("doe")) || u.userName.equals("jdoe")

29. Performances ?
• Byte code is analyzed on first access to Lambda
Expression ( <100ms)
• "Raw" AST is cached for subsequent calls
• Placeholders in AST for captured arguments

30. Part II. Managing data on
MongoDB

31. Managing Data on
MongoDB
• Providing Codecs for Lambda Expressions and
Documents
• Skipping the "DBObject" DTOs layer
MongoDB Java Driver Integration

32. Querying MongoDB
Service
Layer
Lambda
Expression
MongoDB
Java Driver
BSON
Document
MongoDB
FilterExpression
Codec
BSON
Document
Domain
object(s)
Document
Codec

33. Demo #1
Geolocation queries

34. Three more things
(yes, three)

35. Query on Arrays

36. Query on Arrays

37. Query on Arrays
final List<BlogEntry> blogEntries =
blogEntryCollection.filter(
e -> e.comments.elementMatch(
c -> c.author.equals("anonymous") && c.date.greaterOrEquals(twoDaysAgo)))
.toList();
final List<BlogEntry> blogEntries =
blogEntryCollection.filter(
e -> e.comments.author.equals("anonymous") &&
e.comments.date.greaterOrEquals(twoDaysAgo))
.toList();

38. Query Projections

39. Query Projection
Projection Metadata class generation
@Generated(value="o.l.m.a.DocumentAnnotationProcessor")
public abstract class PBlogEntry
implements ProjectionMetadata<BlogEntry> {
@DocumentField(name="_id")
public ProjectionField id;
@DocumentField(name="authorName")
public ProjectionField authorName;
@DocumentField(name="publishDate")
public ProjectionField publishDate;
...
}
@Document(collection="blog")
public class BlogEntry {
@DocumentId
private String id;
@DocumentField
private String authorName;
private Date publishDate;
...
}

40. Query Projection
import static org.lambdamatic.mongodb.Projection.include;
final BlogEntry blogEntry = blogEntries.filter(e -> e.id.equals("1"))
.projection(e -> include(e.authorName, e.title, e.publishDate))
.first();
@Generated(value="o.l.m.a.DocumentAnnotationProcessor")
public abstract class PBlogEntry
implements ProjectionMetadata<BlogEntry> {
@DocumentField(name="_id")
public ProjectionField id;
@DocumentField(name="authorName")
public ProjectionField authorName;
@DocumentField(name="publishDate")
public ProjectionField publishDate;
...
}
public interface Projection {
@IncludeFields
public static void include(final ProjectionField... fields) {}
@ExcludeFields
public static void exclude(final ProjectionField... fields) {}
}

41. Query Projection
Projecting array elements
final BlogEntry blogEntry = blogEntryCollection.filter(e -> e.id.equals("1"))
.projection(e -> include(e.authorName, e.title, e.publishDate,
e.comments.elementMatch(c -> c.author.equals("anonymous") &&
c.date.greaterOrEquals(twoDaysAgo))))
.first();

42. Update Operations

43. Update Operations
@Document(collection="blog")
public class BlogEntry {
@DocumentId
private String id;
/** Name of author of the blog entry. */
private String authorName;
/** Title of the Blog Entry */
private String title;
/** list of comments. */
private List<BlogEntryComment> comments;
...
}
Update Metadata class generation
@Generated(value="o.l.m.a.DocumentAnnotationProcessor")
public abstract class UBlogEntry implements UpdateMetadata<BlogEntry> {
@DocumentField(name="_id")
public String id;
@DocumentField(name="authorName")
public String authorName;
@DocumentField(name="title")
public String title;
@DocumentField(name="comments")
public UBlogEntryCommentArray comments;
...
}

44. Update Operations
BlogEntryComment comment = ... ;
blogEntries.filter(e -> e.id.equals("1")).
forEach(e -> {
e.lastUpdate = new Date();
e.commentsNumber++;
e.comments.push(comment);});
@Document(collection="blog")
public class BlogEntry {
@DocumentId
private String id;
/** date of last update. */
private Date lastUpdate;
/** Number of comments */
private int commentsNumber;
/** list of comments. */
private List<BlogEntryComment> comments;
@EmbeddedDocument
public class BlogEntryComment {
/** comment author. */
private String author;
/** comment date. */
private Date date;
/** comment content. */
private String content;

45. Demo #2
Filter with projections
and Update

46. Project Status
Experimental

47. Project Info
http://github.com/lambdamatic
• Give it a try !
• Clone it / Fork it / Star it
• Open issues to discuss about API and features

48. Thanks !
Q/A