MorphiaUser Guide


Morphia is a Fantom to MongoDB object mapping library.

Morphia is an extension to the Mongo library that maps Fantom objects and their fields to and from MongoDB collections and BSON documents.

Morphia features include:

  • All Fantom literals and BSON types supported by default
  • Support for embedded / nested Fantom objects
  • Extensible mapping - add your own Fantom <-> Mongo converters
  • Optimistic locking support
  • Cursor support

Note: Morphia has no association with Morphia - the Java to MongoDB mapping library. Well, except for the name of course!


Quick Start

  1. Start up an instance of MongoDB:
    C:\> mongod
    MongoDB starting
    db version v5.2.0
    waiting for connections on port 27017
  2. Create a text file called
    using afBson::ObjectId
    using afMorphia::Morphia
    class User {
        @BsonProp ObjectId   _id
        @BsonProp Str        name
        @BsonProp Int        age
        new make(|This| fn) { fn(this) }
    class Example {
        Void main() {
            morphia   := Morphia(`mongodb://localhost:27017/exampledb`)
            datastore := morphia.datastore(User#)
            micky := User {
                it._id  = ObjectId()
                it.age  = 42
       = "Micky Mouse"
            // ---- Create ------
            // ---- Read --------
            mouse := (User) datastore.findOne(true) {
                it->age = 42
            echo(  // --> Micky Mouse
            // ---- Update -----
   = "Minny Mouse"
            // ---- Delete ------
  3. Run as a Fantom script from the command line:
    [afMongo] Found a new Master at mongodb://localhost:27017/exampledb
     _____ ___ ___ ___ ___
    |     | . |   | . | . |
    |_|_|_|___|_|_|_  |___|
    Micky Mouse


MongoDB Connections

A Mongo Connection URL supplies the default database to connect to, along with any user credentials.

Some connection URL options are supported:

  • mongodb://
  • mongodb://

Morphia then uses the connection URL to create a pooled MongoConnMgr.

morphia := Morphia(`mongodb://localhost:27017/exampledb`)


An entity is a top level domain object that is persisted in a MongoDB collection.

Entity objects MUST be annotated with the @Entity facet. By default the MongoDB collection name is the same as the (unqualified) entity type name. Example, if your entity type is acmeExample::User then it maps to a Mongo collection named User. This may be overriden by providing a value for the attribute.

Entity fields are mapped to properties in a MongoDB document. Use the @BsonProp facet to mark fields that should be mapped to / from a Mongo property. Again, the default is to take the property name and type from the field, but it may be overridden by facet values.

As all MongoDB documents define a unique property named _id, all entities must also define a unique property named _id. Example:

class MyEntity {
    ObjectId _id


@Entity { name="AnotherEntity" }
class MyEntity {
    @BsonProp { name="_id" }
    ObjectId wotever

Note that a Mongo Id does not need to be an ObjectId. Any object may be used, it just needs to be unique.


A Datastore wraps a Mongo Collection and is your gateway to saving and reading Fantom objects to / from the MongoDB.

Each Datastore instance is specific to an Entity type, so to create a Datastore you need to specify which Entity it is associated with.

datastore := morhphia.datastore(User#)


At the core of Morphia is a suite of Converters that map Fantom objects to BSON documents.

Standard Converters

Morphia provides support and converters for the following Fantom types:


Map Key Restrictions

As detailed in Restrictions on Field Names MongoDB does not allow the characters $ (dollar) and . (full stop) to be stored in Map keys. To overcome this limitation Morphia automatically encodes keys as unicode escape sequences, similar to how Java works. More specifically, the following characters are escaped:

\uXXXX  -->  \uuXXXX
$       -->  \u0024
.       -->  \u002e

Hence the key "pod.$name-Om\u2126" would be stored as "pod\u002e\u0024name-Om\uu2126".

Morphia automatically decodes Map keys when it reads them back from Mongo, so generally, the encoding / decoding process is of no concern. However, when constructing queries for such key values, it is something you need to be aware of.

Embedded Objects

Morphia is also able to convert embedded, or nested, Fantom objects. Extending the example in Quick Start, here we substitute the Str name for an embedded Name object:

class User {
    @BsonProp ObjectId _id
    @BsonProp Name     name
    @BsonProp Int      age
    new make(|This|in) { in(this) }

class Name {
    @BsonProp Str  firstName
    @BsonProp Str  lastName
    new make(|This|in) { in(this) }


micky := User {
    _id  = ObjectId()
    age  = 42
    name = name {
      firstName = "Micky"
      lastName  = "Mouse"
mongoDoc := datastore.toBsonDoc(micky)

echo(mongoDoc) // --> [_id:xxxx, age:42, name:[lastName:Mouse, firstName:Micky]]

Note that embedded Fantom types need not be annotated with @Entity. The Entity facet is reserved for top level objects only.

Default Values

It is often desirable not to bloat out your database by storing common default values. Perhaps you have a boolean values that is rarely set, or a list that is usually empty? In such situations it can be advantageous to NOT store such values in the database.

To that end, you can set the defVal value on a field's @BsonProp facet.

@BsonProp { defVal=false }
Bool  marker

@BsonProp { defVal=[,] }
Str[] list

Should the field value equal this defVal then it is treated as if it is null, regardless of the field's type nullablity. This, combined with the default null storage strategy result in the value NOT being stored.

When read back from the MongoDB any missing or null values are replaced with defVal.

Mixed Inheritance

Sometimes you want to store a list of mixed embedded classes. Often the list is a mix of different implementations of a common superclass:

SuperClass[] allMixedUp


this.allMixedUp := SuperClass[

This works fine when saving to MongoDb, but when reading the list back Morphia doesn't know which implementation class to create for each item.

To get round this, add a field called _type to SubClassX that stores the implementation type. Morphia will use this to determine which implementation type to create. The easiest way to do this is to just add the following to SuperClass:

class SuperClass {
    Type _type := typeof


Custom Converters

If you want more control over how objects are mapped to and from Mongo, then contribute a custom converter. Do this by implementing BsonConv and pass it to BsonConvs when you constuct it.

Example, to store the Name object as a simple hyphenated string:

using afMorphia::BsonConv
using afMorphia::BsonConvCtx

const class NameConverter : BsonConv {

    override Obj? toBsonVal(Obj? fantomObj, BsonConvCtx ctx) {
        // decide how you want to handle null values
        if (fantomObj == null) return null

        name := (Name) fantomObj
        return "${name.firstName}-${name.lastName}"

    override Obj? fromBsonVal(Obj? bsonVal, BsonConvCtx ctx) {
        // decide how you want to handle null values
        if (bsonVal == null) return null

        vals := ((Str) bsonVal).split('-')
        return Name { it.firstName = vals[0]; it.lastName = vals[1] }

To see it in action:

micky := User {
    it._id  = ObjectId()
    it.age  = 42 = Name {
      it.firstName = "Micky"
      it.lastName  = "Mouse"

bsonConvs := BsonConvs(
    BsonConvs.defConvs {
        it[Name#] = NameConverter
bsonDoc  := bsonConvs.toBsonDoc(micky)

echo(mongoDoc) // --> [_id:xxxx, age:42, name:Micky-Mouse]

Storing Nulls in Mongo

When converting Fantom objects to Mongo, if a Fantom field has the value null should it store a key in the MongoDb with a null value, or should it not store the key at all?

To conserve storage space in MongoDB, by default, Morphia does not store the keys.

If you want to store null values, then pass an option to BsonConvs. Example:

bsonConvs := BsonConvs(null, [
    "storeNullFields" : true

See the BsonConvs ctor and Storing null vs not storing the key at all in MongoDB for more details.

Pickle Mode

Sometimes you wish to read / write objects to Mongo that are outside of your control, meaning their fields won't be annotated with @BsonProp facets. To facilitate this, you can turn on Pickle Mode whereby all non @Transient fields are converted, regardless of any @BsonProp facets. Data from @BsonProp facets, however, will still honoured if defined.

Pickle mode works by automatically writing out _type properties, which are them used when re-inflating objects back.

Pickle Mode may be turned on globally as an option in BsonConvs, or locally as an argument on the @BsonProp facets.

// turn on pickleMode for everything
bsonConvs := BsonConvs(null, [
    "pickleMode" : true

// ... or ...

class User {
    @BsonProp ObjectId _id
    @BsonProp Name     name
    @BsonProp Int      age

    ** Turn on pickleMode just for this field
    ** meta values may be *any* object
    @BsonProp { pickleMode=true }
              Str:Obj? meta

    new make(|This|in) { in(this) }

Optimistic Locking

Think of the following scenario:

  1. User A reads an entity
  2. User B reads the same entity
  3. User B saves their entity
  4. User A saves their entity

Here, User A has just overwritten all User B's changes. To prevent this, Morphia supports optimistic locking.

Optimistic locking is where an entity has a special _version integer property which is incremented everytime an entity is saved. If you attempt to save an entity that has a different _version property to what's in the database (presumably because your entity is out of date) then Morphia throws an OptimisticLockErr.

To use, just define an Int _version field property on your top level entity:

class SomeEntity {

    Int _version


On a successful save. and if the field is non-const, Datastore.update() will increment the _version field on the entity so you may re-save it again without having to re-read it from the database.


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