EWD 3 Training Course Part 22: Traversing Documents using DocumentNode Objects

Copyright © 2016 M/Gateway Developments Ltd
EWD 3 Training Course
Part 22
JavaScript Abstraction of Global Storage:
(c) Traversing Documents
Rob Tweed
Director, M/Gateway Developments Ltd
Twitter: @rtweed

Traversing a Global Node using the cache.node order function:
var node = {
global: 'myGlobal',
subscripts: ['d', 'e2', '' ]
};
var subscript;
do {
subscript = db.order(node).result;
if (subscript !== '') console.log(subscript);
}
while (subscript !== '');
myGlobal("d","e2","f1")="bar1"
"f1", "f2", "f3"
Traversal the hard way

DocumentNode Object method:
forEachChild()
Traversal made easy and intuitive

forEachChild() Method
• Iterates through all child nodes of a
DocumentNode Object
– ie through subscripts in underlying Global
Storage

• Iterates through all child nodes
Storage
– docNode.forEachChild(function(nodeName, childNode) {…});

Storage
– docNode.forEachChild( function(nodeName, childNode) {…}) ;
– Callback function fires on every iteration
• ie every time a child node is found

Storage
Child node's Node Name (ie subscript)

Storage
Child node's Node Name (ie subscript)
DocumentNode object representing the
Child node

myDoc("d","e2","f1")="bar1"
var e2Node = new this.documentStore.DocumentNode('myDoc', ['d', e2']);

e2Node.forEachChild(function(nodeName) {
// do something with the node name / subscript for this iteration
});

// 1st iteration nodeName === 'f1’
});

// 2nd iteration nodeName === 'f2’
});

// 3rd iteration nodeName === 'f3’
});

console.log(nodeName);
});
f1
f2
f3

e2Node.forEachChild(function(nodeName, childNode) {
// do something with the childNode DocumentNode object for this iteration
});

// 1st iteration
});

// 2nd iteration
});

// 3rd iteration
});

// do something with the childNode DocumentNode object for this iteration
});
childNode is a DocumentNode Object, so has all the usual properties and methods

console.log(childNode.value);
});
bar1
bar2
bar3

• Note that because ewd-document-store uses synchronous versions of
underlying cache.node APIs, the call-backs fire in synchronous order
• Additionally, the forEachChild() function will wait until completion before next
command executes
• This greatly simplifies its use!

console.log('start…');
});
console.log('end');
Example
start…
bar1
bar2
bar3
end

console.log('start…');
});
console.log('end');
Example
This can be done safely because QEWD uses
the master / worker architecture of ewd-qoper8
where your handler functions run on their own
in an isolated process

// if callback function returns true (exit boolean flag), it stops the loop
});
Stopping forEachChild() Early

var count = 0;
count++;
if (count === 3) return true;
});
Stopping forEachChild() Early
bar1
bar2

myDoc("a")=123
myDoc("b","c1")="foo"
myDoc("b","c2")="foo2"
myDoc("d","e1","f1a")="bar1a"
myDoc("d","e2","f1b")="bar1b"
Nested forEachChild() loops
Traversal of all nodes and subnodes

myDoc("a")=123
var dNode = new this.documentStore.DocumentNode('myDoc', ['d']);
dNode.forEachChild(function(nodeName, childNode) {
// do something with child node
});

myDoc("a")=123
// 1st iteration
});

myDoc("a")=123
// 1st iteration
childNode.forEachChild(function(nodeName, childNode) {
// do something with grand-child node
});
});

myDoc("a")=123
// 1st iteration
// 1st iteration
});
});

myDoc("a")=123
});
});

myDoc("a")=123
});
});
e1
bar1a
bar2a
e2
bar1b
bar2b
bar3b

myDoc("a")=123
Nest as deeply as you wish
var doc = new this.documentStore.DocumentNode('myDoc');
doc.forEachChild(function(nodeName, childNode) {
// do something with innermost node
});
});
});

myDoc("a")=123
forEachChild() in reverse order?

myDoc("a")=123
forEachChild() in reverse order
var myDoc = new this.documentStore.DocumentNode('myDoc', [ ]);
myDoc.forEachChild( {direction: 'reverse'} , function(nodeName, childNode) {
});
Use optional control object argument

myDoc("a")=123
forEachChild() in reverse order
var myDoc = new this.documentStore.DocumentNode('myDoc', [ ]);
myDoc.forEachChild( {direction: 'reverse'} , function(nodeName, childNode) {
});
d
b
a

myDoc("a")=123
Navigating to Specific Nodes

myDoc("a")=123
var myDoc = new this.documentStore.DocumentNode('myDoc');

myDoc("a")=123
console.log(myDoc.firstChild.value); // 123
firstChild returns a DocumentNode object

myDoc("a")=123
console.log(myDoc.firstChild.value); // 123
console.log(myDoc.firstChild.name); // a
firstChild returns a DocumentNode object

myDoc("a")=123
console.log(myDoc.lastChild.name); // d
lastChild also returns a DocumentNode object

myDoc("a")=123
console.log(myDoc.firstChild.nextSibling.name); // b
nextSibling returns a DocumentNode object

myDoc("a")=123
console.log(myDoc.lastChild.previousSibling.name); // b
previousSibling returns a DocumentNode object

EWD 3 Training Course Part 22: Traversing Documents using DocumentNode Objects

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EWD 3 Training Course Part 22: Traversing Documents using DocumentNode Objects