EWD 3 Training Course Part 20: The DocumentNode Object

Copyright © 2016 M/Gateway Developments Ltd
EWD 3 Training Course
Part 20
JavaScript Abstraction of Global Storage:
(a) The DocumentNode Object
Rob Tweed
Director, M/Gateway Developments Ltd
Twitter: @rtweed

Underlying Concept

myGlobal("a")=123
myGlobal("b","c1")="foo"
myGlobal("b","c2")="foo2"
myGlobal("d","e1","f1")="bar1"
myGlobal
"a" 123
"b"
"c2" "foo2"
"d"
"c1" "foo"
"e2"
"e1"
"f2" "bar2"
"f1" "bar1"
"f2" "bar2"
"f1" "bar1"
"f3" "bar3"
Hierarchical diagram representing a Global

myGlobal = {
a: 123,
b: {
c1: 'foo',
c2: 'foo2'
}
d: {
e1: {
f1: 'bar1',
f2: 'bar2'
},
e2: {
f1: 'bar1',
f2: 'bar2',
f3: 'bar3'
}
}
}
myGlobal("a")=123
One to one correspondence between any tree of Global nodes
and a Javascript object

myGlobal = {
a: 123,
b: {
c1: 'foo',
c2: 'foo2'
}
d: {
e1: {
f1: 'bar1',
f2: 'bar2'
},
e2: {
f1: 'bar1',
f2: 'bar2',
f3: 'bar3'
}
}
}
myGlobal("a")=123
Subscript <=> Property

myGlobal("d","e2","f3") <=> myGlobal.d.e2.f3
Global Node JavaScript Object

But…
JavaScript Objects are in memory
Global Nodes are persistent, on disk

Could we abstract Global Nodes as
Persistent JavaScript Objects?

ewd-document-store
- JavaScript Abstraction of Global Storage
https://github.com/robtweed/ewd-document-store
Layered on top of the basic cache.node APIs

ewd-document-store
Loaded automatically into QEWD workers

ewd-document-store
Made accessible in QEWD by this.documentStore

ewd-document-store
Made accessible in QEWD by this.documentStore
Can also be used standalone for testing and debugging

ewd-document-store
Use in a test harness:
See example in:
https://github.com/robtweed/ewd-document-store/blob/master/lib/tests/CacheStandalone.js

Edit CacheStandalone.js
var DocumentStore = require('ewd-document-store');
var interface = require('cache');
var db = new interface.Cache();
console.log('db: ' + JSON.stringify(db));
// Change these parameters to match your GlobalsDB or Cache system:
var ok = db.open({
path: '/opt/cache/mgr',
username: '_SYSTEM',
password: 'SYS',
namespace: 'USER'
});
console.log('ok: ' + JSON.stringify(ok));
var documentStore = new DocumentStore(db);
console.log(db.version());
var rob = new documentStore.DocumentNode('rob');

Edit CacheStandalone.js
var ok = db.open({
path: 'C:InterSystemsCache2015-2mgr',
password: 'SYS',
namespace: 'USER'
});

Save as
C:qewddocStoreTest.js
var ok = db.open({
password: 'SYS',
namespace: 'USER'
});

Version for use with GT.M
var interface = require('nodem');
var db = new interface.Gtm();
var ok = db.open();

Version for use with ewd-redis-globals
var interface = require('ewd-redis-globals');
var db = new interface();
var ok = db.open();

Run it
cd qewd (or cd /qewd )
node docStoreTest

Run it
cd ewd3
node docStoreTest
It runs a set of examples using DocumentNode objects
You can use it as the basis of your own test harness

Adapting your own test harness
var ok = db.open({
password: 'SYS',
namespace: 'USER'
});
// delete and replace everything from this point onwards
// documentStore provides you with the abstracted interface to your database
// use this to try out the following examples for yourself
// simply replace this.documentStore with documentStore

The DocumentNode Object

DocumentNode Object
var dnode = new documentStore.DocumentNode(name, subscripts);
when using standalone test harness

DocumentNode Object
var dnode = new this.documentStore.DocumentNode(name, subscripts);
when using QEWD

DocumentNode Object
Represents a node within a document store hierarchy
May or may not physically exist at this point
ie this does NOT create a node

DocumentNode Object
Represents a node within a document's hierarchy
May or may not physically exist at this point
ie this does NOT create a node
Creates an instance of an object that represents that node, with
a set of methods and properties to manipulate and access that node

DocumentNode Object
var dnode = new this.documentStore.DocumentNode('myDoc', ['d', 'e2']);
represents myDoc("d","e2")

DocumentNode Object
create: dnode.value = 'foo2';

DocumentNode Object
get: var x = dnode.value;

DocumentNode Object
value is a read/write property

DocumentNode Object
delete: dnode.delete();

DocumentNode Object
Note: delete will also delete any lower-level DocumentNodes
in the underlying Global Storage tree

DocumentNode Object
exists?: var exists = dnode.exists; // true | false

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

var dnode = new this.documentStore.DocumentNode('myDoc', ['d']);
dnode.hasChildren // true
dnode.hasValue // false
dnode.exists // true
myDoc("a")=123

dnode.hasChildren // true
myDoc("a")=123

var dnode = new this.documentStore.DocumentNode('myDoc', ['d', 'e2', 'f3']);
dnode.hasChildren // false
dnode.hasValue // true
myDoc("a")=123

dnode.hasChildren // false
dnode.exists // false
Even though the node doesn’t physically exist, you can define a
DocumentNode Object for it
myDoc("a")=123

dnode.name // f3 Node Name === last global subscript
dnode.parent // myDoc("d","e2")
myDoc("a")=123
Returns a DocumentNode Object

dnode.firstChild // myDoc("d","e2","f1")
dnode.lastChild // myDoc("d","e2","f3")
dnode.previousSibling // myDoc("d","e1")
dnode.nextSibling // undefined
myDoc("a")=123
DocumentNode
Objects

DocumentNode Object
• We’ll further explore it in subsequent parts
of this course
• For more / additional information:
– http://gradvs1.mgateway.com/download/ewd-document-store.pdf

EWD 3 Training Course Part 20: The DocumentNode Object

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