datamodeljs
v1.3.2
Published
This library handles entity like javascript objects. Allowing relationships between those objects. Also allowing bi-directional relationships. Tracking states (changed, new, deleted) of those objects.
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datamodeljs
Data Model Management Library for JavaScript
The main goal of datamodeljs is to ensure a consistent and reliable data structure when communicating with a backend service.
In all projects the data structure between backend and frontend can be considered as an interface contract. If either side changes the structure of the data - the counterpart has problems validating and handling the data.
In order to avoid long lasting debugging sessions in a JavaScript application we use datamodeljs to read in and validate the delivered data against the defined entity model classes.
A secondary goal of datamodeljs is the ability to manage entity objects and keep track of their states (e.g. newly created, marked as changed, marked for deletion)
This entity object management allows the JavaScript application to manipulate business objects on block before sending them anywhere.
In order to be able to handle complex business objects datamodeljs implements a bi-directional entity model. Examples can be seen in "Defining entity classes"
The Github page contains an interactive example and demonstrates the possibilities with datamodeljs.
Entity object states
Entities created with datamodeljs know their entity class name:
_className
- the string representation of the entities class name (as declared with thedefine
function)
Entities created with datamodeljs also can track four different states:
_isDirty
- has the entity changed on client side since it load time_isDeleted
- is the entity marked for deletion on client side_isTransient
- was the entity created newly on client side_isStub
- is the entity referenced by another entities relationship, but the entity itself was not loaded by now
In most cases a dirty entity leads to an PUT call in the backend. A deleted entity leads a DELETE call. A transient entity results in a POST call and a stub entity should be loaded using a GET call. Mapping this is not part of datamodeljs since it has not the goal to cover the AJAX requests. Mapping the entity states to proper AJAX requests is the applications task.
Entity serialisation and cloning
When serialising or cloning entity objects their internal object properties _className
, _isDirty
, _isDeleted
, _isTransient
and _isStub
are not exposed. So using JSON.stringify before sending entites to a service ensures that no internal property is send to the service. Also cloning entity objects simply creates a new JavaScript object that has the entites properties and values set - but it is not considered an entity object anymore since the internal object properties are not cloned.
Initialization
datamodeljs exposes itself to the global variable 'datamodeljs
'. In case that a different symbol for datamodeljs is needed use the symbol
function. This function allows you to occupy a different global name by giving a new name or releasing the last name by providing no name or an empty name.
datamodeljs.symbol([symbol:String]) : datamodeljs
Example:
// define an alternate global exposure
datamodeljs.symbol("dmjs")
// delete the former alternate global exposure and restore the old value of 'dmjs'
datamodeljs.symbol("")
datamodeljs.symbol()
datamodeljs allows the definition of different dataManager storages by using the dm
function:
datamodeljs.dm(name:String) : dataManager
Example:
var myDataManager = datamodeljs.dm("mine");
// all further examples are working with this dataManager
var dm = datamodeljs.dm("default")
Data management
The dataManager
created by datamodeljs enables the entity class definition and entity management. The following chapters describe the possibilities in detail:
Defining entity classes
Defining an entity class is the basic for working with entities. Entities are defined with the define
function. A class definition needs at least an unique class name (cls
) and its specification (spec
). A parent class name is optional. If a parent class name is given, all attributes of that class will be copied into the new class name. Please be aware that this is no real extends mechanism of those classes.
dataManager.define(cls:String, [parentCls:String], spec:Object) : void
The class specification is a list of attributes following this syntax:
{
(attribute: (primary)?type(arity)? )*
};
- The attribute's name is set by the
attribute
tag. The internal properties_className
,_isDirty
,_isDeleted
,_isTransient
and_isStub
are reserved and can not be used as an class attribute. - One attribute can be defined as
primary
field with the prefix@
. - The attribute's
type
can be eithernumber
,boolean
,string
,object
or any other class name - The
arity
defines this attributes relation as an arrayed relation and it can have different options?
- stands for zero or one(0..1) elements of the giventype
+
- stands for one or more(1..n) elements of the giventype
*
- stands for zero or more(0..n) elements of the giventype
Examples:
dm.define("AbstractData", {
id: '@number', // this is the primary field
version: 'number'
});
dm.define("Verweis", "AbstractData", { // get all attributes of AbstractData copied
verweisTyp: "string",
anzeigename: "string",
knoten: "Knoten" // relation to objects of class Knoten
});
dm.define("Knoten", "AbstractData", {
anzeigename: 'string',
kindKnoten: 'Knoten*', // Knoten can have n childs being Knoten as well
pfad: 'string'
});
Undefining entity classes
Removing a class definition from the dataManager
is possible with the undefine
function:
dataManager.undefine(cls:String) : void
Using this function is removing the class, its specification and all entity objects from the dataManager
. It is most useful when data models are loaded dynamically.
Creating entity objects
Creating objects of entities is available with the create
function.
dataManager.create(cls:String, payload:Object) : entity
- The
cls
must be one of the defined class names within thedataManager
- The
payload
is the JSON object that should be converted into an entity. The given payload is hereby validated against the entity class specification
Example:
dm.create("Verweis", {
id: 1,
version: 1,
verweisTyp: "Symbol",
anzeigename: "symbolic link",
knoten: 1 // it is sufficient to only provide the id of the related object
// the dataManager resolves the relation using the given unique id
})
The given example creates two entity objects. The first is the desired Verweis
. The second object is a Knoten
with id
set to but the flag stub set to true
. Meaning that this object is referenced somewhere but it was not yet loaded. If this objects get loaded and created later on, then the reference to this Knoten
wont change, only its content will be updated and its stub flag will be set to false
.
Example:
dm.create("Knoten", {
id: 1,
version: 1,
anzeigename: "Root Knoten",
kindKnoten: [], // it is ok if this array is empty since the arity is *
pfad: "/"
})
Deleting entity objects
Deleting a single entity object is possible using the destroy
function.
dataManager.destroy(cls:String, obj:Object, [force:Boolean]) : void
The object will be immediatly removed from the dataManager
if it was marked as transient
entity or if force
is set to true
. Otherwise it will be marked as deleted
. This way the JavaScript application can still handle the deletion with a proper AJAX call.
Example:
dm.destroy("Verweis", dm.findById("Verweis", 1))
The deletion of all objects of a given entity class(cls
) is possible using the destroyAll
function.
dataManager.destroyAll(cls:String) : void
Example:
dm.destroyAll("Knoten")
Tracking and changing entity object states
Changing the states of an entity is the JavaScript application's task. Entity attributes can be altered as usual in JavaScript applications. The entity class name _className
can not be changed or deleted from the entity object. The specific entity states _isDirty
, _isDeleted
, _isTransient
and _isStub
can only be altered to a new legal boolean value.
// entity object properties
entityObj._className : String
entityObj._isDirty : Boolean
entityObj._isDeleted : Boolean
entityObj._isTransient : Boolean
entityObj._isStub : Boolean
For backward compatibility the dataManager
functions isDirty
, isDeleted
, isTransient
and isStub
still remain as decprecated functions (see documentation in release 1.1.0#tracking-and-changing-entity-object-states).
Finding entity objects
Finding entities can be reached over several ways
findAll
- find all objects of a given entity classfindAllDirty
- find all objects of a given entity class that are marked asdirty
findAllDeleted
- find all objects of a given entity class that are marked asdeleted
findAllTransient
- find all objects of a given entity class that are marked astransient
findAllStub
- find all objects of a given entity class that are marked asstub
findById
- find all objects of a given entity class that match the given primary keyfindByExample
- find all objects of a given entity class that match a given example object
The following finder functions only need the class name (cls
) and will return an array of entity objects that match the finder.
dataManager.findAll(cls:String) : Array(entity)
dataManager.findAllDirty(cls:String) : Array(entity)
dataManager.findAllDeleted(cls:String) : Array(entity)
dataManager.findAllTransient(cls:String) : Array(entity)
dataManager.findAllStub(cls:String) : Array(entity)
Example:
dm.findAll("Verweis")
dm.findAllDirty("Knoten")
dm.findAllDeleted("Knoten")
dm.findAllTransient("Knoten")
dm.findAllStub("Knoten")
Finding entities by primary key is quite easy by providing the desired primary as additional parameter (id
). The id
is defined as Any
since it depends on the class specification. Basically it is either a string
or a number
.
dataManager.findById(cls:String, id:Any) : entity
Example:
dm.findById("Verweis", 1)
Finding entities by a given example
object is available via the findByExample
function.
dataManager.findByExample(cls:String, example:Object) : Array(entity)
Example:
// find all Verweis entities where verweisTyp is equal to "Symbol"
dm.findByExample("Verweis", { verweisTyp: "Symbol" })
// find all Verweis entities where verweisTyp is equal to "Symbol" and knoten is equal to Knoten with id 1
dm.findByExample("Verweis", { verweisTyp: "Symbol", knoten: 1 })
Partial entity import
Sometimes it is useful or necessary to import data into existing entity objects. The problem with this is that any existing relationship with other others or from other objects should not be influenced. Importing data fields into an existing entity is possible with the import
function. A given example object (example
) will hereby be merged into an existing entity object (obj
).
dataManager.import(cls:String, obj:Object, example:Object) : entity
Example:
dm.import("Verweis", dm.findById("Verweis", 1), { verweisTyp: "Copy", anzeigename: "Partial change" })
This is often needed, if a JavaScript application edits entities then stores changes to any other system and gets a newly changed object as result back. In this case the old 'saved' object still exists in the dataManager
and it must be updated with the new result of the service.
Debugging entity class and objects
Since the dataManager
does quite some jobs for us and a data model might be slightly huge and complex datamodeljs enables a little debugging help for developers.
dataManager.dump() : void
Using the dump
function on the dataManager
shows you two lists with information:
- a full list of all defined classes and their specification
- a full list of all defined entity objects ordered by class
once as an arrayed list
and once as an object map allowing access by primary key
So at any time during development, application test and application runtime it should be possible to get an insight to what the dataManager
handles.