Following advice from this question I keep custom attributes in a central place using a _data object.
Setting attributes using set doesn't work like expected.
var opts = {
'width': 200,
'height': 200,
_data:{'key':'oldvalue'}
};
var rect = new fabric.Rect(opts);
rect.set('_data.key', 'newvalue')
//rect.get('_data.key') will still return 'oldvalue'
It seems obvious that set uses _data.key as string - but is there any other way?
Of course i can do rec._data.key = 'newvalue'...
using this approach for now:
var _data = rect.get('_data')
_data.key = 'newvalue'
rect.set('_data', _data)
You can use any key name in a fabric object set method. But in a typescript project the editor will complain because the interfaces for the Object class don't have these properties.
The interface "Object" extends the interface "IObjectOptions", which includes the properties that belong to the fabric base Object. There are two properties (name and data) that can be used to add custom properties. name must be a string, and data can be anything.
Here's the snippet within the IObjectOptions interface:
/**
* Not used by fabric, just for convenience
*/
name?: string;
/**
* Not used by fabric, just for convenience
*/
data?: any;
Example:
rect.set('name', 'myname');
rect.set('data', {
'key1':'value1',
'key2':'value2',
'key3':'value3'
});
Related
I'm trying to find a nice way to validate a body using DTO (using the brilliant class-validator and class-transformer libraries). It works really well, even for nested structures but in my case I'd like to have the body property based on some conditions.
Example that will probably help to understand:
Let's imagine my body should always have selectedCategory.
Based on that field, the content could either be from category 1, which contains prop1 OR from category 2, which contains prop2.
I do not want to allow a null for both of them, I really want to have to either have prop1 defined or prop2 based on the selectedCategory.
I think that I could use a pipe, but then how can I specify the correct DTO to use?
I've built a "base" class with all the common properties and few other classes that inherit from it.
I could instantiate the pipe manually based on the property selectedCategory, that'd be ideal but I have no clue what to pass as a second argument of the pipe (metadata).
Thanks for your help.
Have you tried using groups?
Instead of having multiple DTOs, you just create one DTO. Every property is assigned to one or multiple groups:
#Min(12, {groups: ['registration', 'update']})
age: number;
#Length(2, 20, {groups: ['registration']})
name: string;
You can then conditionally pass the groups to class transformer / validator:
#Injectable()
export class ConditionalValidationPipe implements PipeTransform {
async transform(entity: any, metadata: ArgumentMetadata) {
// Dynamically determine the groups
const groups = [];
if (entity.selectedCategory === 1) {
groups.push('registration');
}
// Transform to class with groups
const entityClass = plainToClass(EntityDto, entity, { groups })
// Validate with groups
const errors = await validate(entityClass, { groups });
if (errors.length > 0) {
throw this.createError(errors);
}
return entityClass;
}
}
Have you tried the ValidateIf statement?
You can have multiple validations for props1 or props2 and apply them if selectedCategory is "category 1" or "category 2" accordingly.
I have data coming from an external source that I want to process. In order to do that, the objects I'm receiving are tagged with their original class name. Now I want to take that tag name and use it to populate a model in my own application. I'm stuck at the step where I check for that class having an equivalent in my codebase. Its going to look something like this:
this.objects.forEach((object) => {
if (typeof object.class_tag !== 'undefined') { //the problem line
//create class instance
}
});
In php I'd simply call class_exists to achieve this
<?php
if (class_exists($object->class_tag)) {}
What is the correct approach here?
I don't see the clear way to do this in a just one line.
One of the possible approaches is the way you register your existing classes.
For example if you use some kind of a namespace later on you can simply check the class for existance in the namespace.
Sample code:
class A {}
const a = "A"
const namespace = { A };
if (namespace[a]) {
// class exists, you can create object
const instance = new namespace[a]();
}
Probably, much better approach would be to make some service, that will registerClass, checkClass and createInstance for you. So your logic is wrapped in one place.
I found a way of doing it
(credit to https://stackoverflow.com/a/34656123/746549)
let logger = require('../javascripts/serverlog');
let util = require('util');
let Extension = require('../models/object/Extension');
const classes = {Extension: Extension};
/**
* Utility to emulate class exists / dynamic class naming
* #param className
* #returns {*}
*/
module.exports.dynamicClass = (className) => {
logger.debug(classes);
logger.debug(className);
if (classes[className]) {
return classes[className];
} else {
return false;
}
};
Usage:
let ClassOrFalse = dynamicClass.dynamicClass(object._class_tag);
var method = 'serviceName.MethodName'
I Just want to call it like
serviceName.methodName(function(output callback){
});
Is there any approach to call it.thanks
There are two methods that I can think of now.
JS eval
You can use the javascript eval function to convert any string into code snippet like below. Although eval is a quick solution but should not be used unless you dont have any other option by your side.
var method = 'UserService.getData';
eval(method)();
Factory pattern
Use a below pattern to get the service
You would need to define the services in such a manner that you can access them using a pattern.
var Services = {
// UserService and AccountsService are again objects having some callable functions.
UserService : {getData: function(){}, getAge: function(){}},
AccountsService : {getData: function(){}, getAge: function(){}},
// getService is the heart of the code which will get you the required service depending on the string paramter you pass.
getService : function(serviceName){
var service = '';
switch(serviceName){
case 'User':
service = this.UserService;
break;
case 'Accounts':
service = this.AccountsService;
break;
}
return service;
}
}
You can use get the required service with below code
Services.getService('User')
I'm not aware of any way you can resolve the serviceName part of that string to an object, without using eval. So obviously you need to be extremely careful.
Perhaps:
if (method.match(/^[a-zA-Z0-9_]+\.[a-zA-Z0-9_]+$/) {
var servicePart = eval(method.split('.')[0]);
var methodPart = method.split('.')[1];
servicePart[methodPart](...)
}
There are two separate problems in your question:
How to access object property by property name (string)?
How to access object by it's name (string)?
Regarding the first problem - it is easy to access object property by string using the following notation:
const myObject = {
myProp: 1,
};
console.log(myObject['myProp']);
And regarding the second problem - it depends on what serviceName is:
if it is a property of some other object, then use someObject['serviceName']['MethodName']
if it is a local variable, consider using a Map (https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map) to associate strings with objects;
How do we use 'inheritance' in Node.JS? I heard that prototype is similar to interfaces in java. But I have no idea how to use it!
Although there are various ways of performing inheritance and OO in javascript, in Node.js you would typically use the built in util.inherits function to create a constructor which inherits from another.
See http://book.mixu.net/ch6.html for a good discussion on this subject.
for example:
var util = require("util");
var events = require("events");
function MyOwnClass() {
// ... your code.
}
util.inherits(MyOwnClass, events.EventEmitter);
Creating an object constructor in pure JS:
They're just functions like any other JS function but invoked with the new keyword.
function Constructor(){ //constructors are typically capitalized
this.public = function(){ alert(private); }
var private = "Untouchable outside of this func scope.";
}
Constructor.static = function(){ alert('Callable as "Constructor.static()"'); }
var instance = new Constructor();
Inheritance:
function SubConstructor(){
this.anotherMethod(){ alert('nothing special'); }
}
function SubConstructor.prototype = new Constructor();
var instance = new SubConstructor();
instance.public(); //alerts that private string
The key difference is that prototypal inheritance comes from objects, rather than the things that build them.
One disadvantage is that there's no pretty way to write something that makes inheritance of instance vars like private possible.
The whopping gigantor mega-advantage, however, is that we can mess with the prototype without impacting the super constructor, changing a method or property for every object even after they've been built. This is rarely done in practice in higher-level code since it would make for an awfully confusing API but it can be handy for under-the-hood type stuff where you might want to share a changing value across a set of instances without just making it global.
The reason we get this post-instantiated behavior is because JS inheritance actually operates on a lookup process where any method call runs up the chain of instances and their constructor prototype properties until it finds the method called or quits. This can actually get slow if you go absolutely insane with cascading inheritance (which is widely regarded as an anti-pattern anyway).
I don't actually hit prototype specifically for inheritacne a lot myself, instead preferring to build up objects via a more composited approach but it's very handy when you need it and offers a lot of less obvious utility. For instance when you have an object that would be useful to you if only one property were different, but you don't want to touch the original.
var originInstance = {
originValue:'only on origin',
theOneProperty:'that would make this old object useful if it were different'
}
function Pseudoclone(){
this.theOneProperty = "which is now this value";
}
Pseudoclone.prototype = originInstance;
var newInstance = new Psuedoclone();
//accesses originInstance.originValue but its own theOneProperty
There are more modern convenience methods like Object.create but only function constructors give you the option to encapsulate private/instance vars so I tend to favor them since 9 times out of 10 anything not requiring encapsulation will just be an object literal anyway.
Overriding and Call Object Order:
( function Constructor(){
var private = "public referencing private";
this.myMethod = function(){ alert(private); }
} ).prototype = { myMethod:function(){ alert('prototype'); };
var instance = new Constructor();
instance.myMethod = function(){ alert(private); }
instance.myMethod();//"undefined"
Note: the parens around the constructor allow it to be defined and evaluated in one spot so I could treat it like an object on the same line.
myMethod is alerting "undefined" because an externally overwritten method is defined outside of the constructor's closure which is what effective makes internal vars private-like. So you can replace the method but you won't have access to what it did.
Now let's do some commenting.
( function Constructor(){
var private = "public referencing private";
this.myMethod = function(){ alert(private); }
} ).prototype = { myMethod:function(){ alert('prototype'); };
var instance = new Constructor();
//instance.myMethod = function(){ alert(private); }
instance.myMethod();//"public referencing private"
and...
( function Constructor(){
var private = "public referencing private";
//this.myMethod = function(){ alert(private); }
} ).prototype = { myMethod:function(){ alert('prototype'); };
var instance = new Constructor();
//instance.myMethod = function(){ alert(private); }
instance.myMethod();//"prototype"
Note that prototype methods also don't have access to that internal private var for the same reason. It's all about whether something was defined in the constructor itself. Note that params passed to the constructor will also effectively be private instance vars which can be handy for doing things like overriding a set of default options.
Couple More Details
It's actually not necessary to use parens when invoking with new unless you have required parameters but I tend to leave them in out of habit (it works to think of them as functions that fire and then leave an object representing the scope of that firing behind) and figured it would be less alien to a Java dev than new Constructor;
Also, with any constructor that requires params, I like to add default values internally with something like:
var param = param || '';
That way you can pass the constructor into convenience methods like Node's util.inherit without undefined values breaking things for you.
Params are also effectively private persistent instance vars just like any var defined in a constructor.
Oh and object literals (objects defined with { key:'value' }) are probably best thought of as roughly equivalent to this:
var instance = new Object();
instance.key = 'value';
With a little help from Coffeescript, we can achieve it much easier.
For e.g.: to extend a class:
class Animal
constructor: (#name) ->
alive: ->
false
class Parrot extends Animal
constructor: ->
super("Parrot")
dead: ->
not #alive()
Static property:
class Animal
#find: (name) ->
Animal.find("Parrot")
Instance property:
class Animal
price: 5
sell: (customer) ->
animal = new Animal
animal.sell(new Customer)
I just take the sample code Classes in CoffeeScript. You can learn more about CoffeeScript at its official site: http://coffeescript.org/
I have an existing application that sends a Request with a parameter named 'filters'. The 'filters' parameter contains a string that is JSON encoded. Example:
[{"dataIndex":"fieldName", "value":"fieldValue"}, {"dataIndex":"field2", "value":"value2"}].
Using ServiceStack, I would like to bind this as a property on a C# object (class Grid). Is there a preferred method to handle this? Here are the options I can think of. I don't think either 'feel' correct.
Option 1:
I do have a 'ServiceModel' project and this would create a dependency on it which I don't really like.
In AppHost.Configure() method add
RequestBinders[typeof(Grid)] => httpReq => {
return new Grid() {
Filters = new ServiceStack.Text.JsonSerializer<IList<Filter>>().DeserializeFromString(httpReq.QueryString["filters"])
}
}
Option 2:
Seems kind of 'hacky'
public class Grid
{
private string _filters;
public dynamic Filters {
get
{
ServiceStack.Text.JsonSerializer<IList<Filter().DeserializeFromString(_filters);
}
set
{
_filters = value;
}
}
}
You can send Complex objects in ServiceStack using the JSV Format.
If you want to send JSON via the QueryString you can access it from inside your Service of Request filters with something like:
public object Any(Request req) {
var filters = base.Request.QueryString["Filters"].FromJson<List<Filter>>();
}
Note: Interfaces on DTOs are bad practice.