EWD 3 Training Course Part 21: Persistent JavaScript Objects

Copyright © 2016 M/Gateway Developments Ltd
EWD 3 Training Course
Part 21
JavaScript Abstraction of Global Storage:
(b) Persistent JavaScript Objects
Rob Tweed
Director, M/Gateway Developments Ltd
Twitter: @rtweed

var myDoc = new this.documentStore.DocumentNode( 'myDoc');
myDoc("a")=123
myDoc("b","c1")="foo"
myDoc("b","c2")="foo2"
myDoc("d","e1","f1")="bar1"

Can we then refer to: myDoc.d.e2.f3 ?
myDoc("a")=123

myDoc.d.e2.f3
Is a DocumentNode Object
myDoc("a")=123

myDoc.d.e2.f3
myDoc("a")=123
Would also have to be a DocumentNode Object
This would mean we'd have to know that the 'd' property was, or could be, a valid node

myDoc.d.e2.f3
myDoc("a")=123
Would also have to be a DocumentNode Object

myDoc.d.e2.f3
BUT: Impossible to predict or determine in advance all the
possible subscripts of a Global
myDoc("a")=123

myDoc.d.e2.f3
•No schema to tell us
myDoc("a")=123

myDoc.d.e2.f3
•No schema to tell us
•could be hundreds of thousands, or millions of subscript values
and any number of levels of hierarchy
myDoc("a")=123

myDoc.x.value
Also: can't create properties automatically using subscript names
as these might clash with DocumentNode property or method names
as in the case above
myDoc("a")=123
myDoc("x","value")="hello world"

$() Function
var myDoc = new this.documentStore.DocumentNode('myDoc');
var dNode = myDoc.$('d');
myDoc("a")=123

$() Function
myDoc("a")=123
$():
- Returns a DocumentNode Object representing the specified sub-node
of the parent DocumentNode

$() Function
var dNode = new this.documentStore.DocumentNode('myDoc', [ 'd']);
This does the same thing, but is much more verbose
myDoc("a")=123

Chaining $() Functions
myDoc("a")=123

var e2Node = dNode.$('e2');
myDoc("a")=123

var e2Node = myDoc.$('d').$('e2');
Does the same thing by chaining
myDoc("a")=123

var f3Node = myDoc.$('d').$('e2').$('f3');
myDoc("a")=123

$() only needs invoking once
myDoc("a")=123
A DocumentNode represented by $d was instantiated as a property of
the myDoc DocumentNode

myDoc("a")=123
A DocumentNode represented by $d was instantiated as a property of
the myDoc DocumentNode
Now accessible as myDoc.$d

myDoc("a")=123
A DocumentNode represented by $e2 was instantiated as a property of myDoc.$d

myDoc("a")=123
A DocumentNode represented by $e2 was instantiated as a property of myDoc.$d
Now accesible as myDoc.$d.$e2

myDoc("a")=123
Only need to use $() once for any specific subscript

myDoc("a")=123
So we don’t need to do this

var f2Node = myDoc.$d.$e2.$('f2');
myDoc("a")=123
We can do this instead, provided $() has been
used previously for the specified subscript

$ properties are DocumentNodes
var f3Value = f3Node.value; // bar3
myDoc("a")=123

var f3Value = myDoc.$d.$e2.$f3.value; // bar3
myDoc("a")=123

myDoc.$d.$e2.$f3.value = 'New value';
myDoc("a")=123

Persistent JavaScript Objects!
myDoc.$d.$e2.$f3.value = 'New value';
myDoc("a")=123
myDoc("d","e2","f3")=”New value"
Updates value on disk, not an in-memory copy
"Persistent JavaScript Objects"

Persistent JavaScript Objects
myDoc("a")=123
myDoc("d","e2","f3")=”New value"
Not quite: myDoc.d.e2.f3
Instead: myDoc.$d.$e2.$f3
But no chance of subscript-based properties clashing with
DocumentNode property or method names by prefixing with $

EWD 3 Training Course Part 21: Persistent JavaScript Objects

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EWD 3 Training Course Part 21: Persistent JavaScript Objects