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I am trying to create an interface for traversing tables in a relation database. Each select represents a column. If the column is a foreign key, a new select is added to the right. This keeps happening for every foreign key that the user accesses. The number of selects is dynamic.
I made a buggy implementation that has code that manually adds and removes select views. I think it probably can be replaced with better Ember code (some kind of array object maybe?), I'm just not sure how to best use the framework for this problem.
Here's my JSBin http://jsbin.com/olefUMAr/3/edit
HTML:
<!DOCTYPE html>
<html>
<head>
<meta name="description" content="Ember template" />
<meta charset=utf-8 />
<title>JS Bin</title>
<script src="http://code.jquery.com/jquery-1.9.0.js"></script>
<script src="http://builds.emberjs.com/handlebars-1.0.0.js"></script>
<script src="http://builds.emberjs.com/tags/v1.1.2/ember.js"></script>
</head>
<body>
<script type="text/x-handlebars" data-template-name="my_template">
{{view fieldSelects}}
</script>
<div id="main"></div>
</body>
</html>
JavaScript:
App = Ember.Application.create();
var TemplatedViewController = Ember.Object.extend({
templateFunction: null,
viewArgs: null,
viewBaseClass: Ember.View,
view: function () {
var controller = this;
var viewArgs = this.get('viewArgs') || {};
var args = {
template: controller.get('templateFunction'),
controller: controller
};
args = $.extend(viewArgs, args);
return this.get('viewBaseClass').extend(args);
}.property('templateFunction', 'viewArgs'),
appendView: function (selector) {
this.get('view').create().appendTo(selector);
},
appendViewToBody: function () {
this.get('view').create().append();
}
});
var DATA = {};
DATA.model_data = {
"Book": {
"fields": [
"id",
"title",
"publication_year",
"authors"
],
"meta": {
"id": {},
"title": {},
"publication_year": {},
"authors": {
"model": "Author"
}
}
},
"Author": {
"fields": [
"id",
"first_name",
"last_name",
"books"
],
"meta": {
"id": {},
"first_name": {},
"last_name": {},
"books": {
"model": "Book"
}
}
}
};
var Controller = TemplatedViewController.extend({
view: function () {
var controller = this;
return this.get('viewBaseClass').extend({
controller: controller,
templateName: 'my_template'
});
}.property(),
selectedFields: null,
fieldSelects: function () {
var filter = this;
return Ember.ContainerView.extend({
controller: this,
childViews: function () {
var that = this;
var selectedFields = filter.get('selectedFields');
var ret = [];
var model = 'Book';
selectedFields.forEach(function (item, index, enumerable) {
var selection = item;
if (model) {
var select = that.makeSelect(model, that.getPositionIndex(), selection, true).create();
ret.pushObject(select);
model = DATA.model_data[model].meta[selection].model;
}
});
return ret;
}.property(),
nextPositionIndex: 0,
incrementPositionIndex: function () {
this.set('nextPositionIndex', this.get('nextPositionIndex') + 1);
},
getPositionIndex: function () {
var index = this.get('nextPositionIndex');
this.incrementPositionIndex();
return index;
},
setNextPositionIndex: function (newValue) {
this.set('nextPositionIndex', newValue+1);
},
makeSelect: function (modelName, positionIndex, selection, isInitializing) {
var view = this;
return Ember.Select.extend({
positionIndex: positionIndex,
controller: filter,
content: DATA.model_data[modelName].fields,
prompt: '---------',
selection: selection || null,
selectionChanged: function () {
var field = this.get('selection');
// Remove child views after this one
var lastIndex = view.get('length') - 1;
if (lastIndex > this.get('positionIndex')) {
view.removeAt(this.get('positionIndex')+1, lastIndex-this.get('positionIndex'));
view.setNextPositionIndex(this.get('positionIndex'));
}
if (! isInitializing && DATA.model_data[modelName].meta[field].model) {
var relatedModel = DATA.model_data[modelName].meta[field].model;
view.pushObject(view.makeSelect(relatedModel, view.getPositionIndex()).create());
}
// Reset ``isInitializing`` after the first run
if (isInitializing) {
isInitializing = false;
}
var selectedFields = [];
view.get('childViews').forEach(function (item, index, enumerable) {
var childView = item;
var selection = childView.get('selection');
selectedFields.pushObject(selection);
});
filter.set('selectedFields', selectedFields);
}.observes('selection')
});
}
});
}.property()
});
var controller = Controller.create({
selectedFields: ['authors', 'first_name']
});
$(function () {
controller.appendView('#main');
});
233
I would tackle this problem using an Ember Component. I have used a component because it will be:
Easily reusable
The code is self contained, and has no external requirements on any of your other code.
We can use plain javascript to create the view. Plain javascript should make the code flow easier to understand (because you don't have to know what Ember is doing with extended objects behind the scenes), and it will have less overhead.
I have created this JSBin here, of the code below.
Add to your handlebars template:
{{select-filter-box data=model selected=selected}}
Create a select-filter-box tag and then bind your model to the data attribute, and your selected value array to the selected attribute.
The application:
App = Ember.Application.create();
App.ApplicationController = Ember.ObjectController.extend({
model: DATA.model_data,
selected: ['Author','']
});
App.SelectFilterBoxComponent = Ember.Component.extend({
template: Ember.Handlebars.compile(''), // Blank template
data: null,
lastCount: 0,
selected: [],
selectedChanged: function(){
// Properties required to build view
var p = this.getProperties("elementId", "data", "lastCount", "selected");
// Used to gain context of controller in on selected changed event
var controller = this;
// Check there is at least one property. I.e. the base model.
var length = p.selected.length;
if(length > 1){
var currentModelName = p.selected[0];
var type = {};
// This function will return an existing select box or create new
var getOrCreate = function(idx){
// Determine the id of the select box
var id = p.elementId + "_" + idx;
// Try get the select box if it exists
var select = $("#" + id);
if(select.length === 0){
// Create select box
select = $("<select id='" + id +"'></select>");
// Action to take if select is changed. State is made available through evt.data
select.on("change", { controller: controller, index: idx }, function(evt){
// Restore the state
var controller = evt.data.controller;
var index = evt.data.index;
var selected = controller.get("selected");
// The selected field
var fieldName = $(this).val();
// Update the selected
selected = selected.slice(0, index);
selected.push(fieldName);
controller.set("selected", selected);
});
// Add it to the component container
$("#" + p.elementId).append(select);
}
return select;
};
// Add the options to the select box
var populate = function(select){
// Only populate the select box if it doesn't have the correct model
if(select.data("type")==currentModelName)
return;
// Clear any existing options
select.html("");
// Get the field from the model
var fields = p.data[currentModelName].fields;
// Add default empty option
select.append($("<option value=''>------</option>"));
// Add the fields to the select box
for(var f = 0; f < fields.length; f++)
select.append($("<option>" + fields[f] + "</option>"));
// Set the model type on the select
select.data("type", currentModelName);
};
var setModelNameFromFieldName = function(fieldName){
// Get the field type from current model meta
type = p.data[currentModelName].meta[fieldName];
// Set the current model
currentModelName = (type !== undefined && type.model !== undefined) ? type.model : null;
};
// Remove any unneeded select boxes. I.e. where the number of selects exceed the selected length
if(p.lastCount > length)
for(var i=length; i < p.lastCount; i++)
$("#" + p.elementId + "_" + i).remove();
this.set("lastCount", length);
// Loop through all of the selected, to build view
for(var s = 1; s < length; s++)
{
// Get or Create select box at index s
var select = getOrCreate(s);
// Populate the model fields to the selectbox, if required
populate(select);
// Current selected
var field = p.selected[s];
// Ensure correct value is selected
select.val(field);
// Set the model for next iteration
setModelNameFromFieldName(field);
if(s === length - 1 && type !== undefined && type.model !== undefined)
{
p.selected.push('');
this.notifyPropertyChange("selected");
}
}
}
}.observes("selected"),
didInsertElement: function(){
this.selectedChanged();
}
});
The component takes the two parameters model and selected then binds an observer onto the selected property. Any time the selection is changed either through user interaction with the select boxes, or by the property bound to selected the view will be redetermined.
The code uses the following approach:
Determine if the selection array (selected) is greater than 1. (Because the first value needs to be the base model).
Loop round all the selected fields i, starting at index 1.
i exists. If not create a select box.i has the right model fields based on the current populated model. If yes, do nothing, if not populate the fields.When a select box is created, an onchange handler is hooked up to update the selected value by slicing the selected array right of the current index and adding its own value. This will cause the view to change as required.
A property count keeps track of the previous selected's length, so if a change is made to a selection that decreases the current selected values length, then the unneeded select boxes can be removed.
The source code is commented, and I hope it is clear, if you have any questions of queries with how it works, feel free to ask, and I will try to explain it better.
Having looked at your model, have you considered simplifying it to below? I appreciate that you may not be able to, for other reasons beyond the scope of the question. Just a thought.
DATA.model_data = {
"Book": {
"id": {},
"title": {},
"publication_year": {},
"authors": { "model": "Author" }
},
"Author": {
"id": {},
"first_name": {},
"last_name": {},
"books": { "model": "Book" }
}
};
So field names would be read off the object keys, and the value would be the meta data.
I hope you find this useful. Let me know if you have any questions, or issues.
You can use any controller you want with this component. In my demo of the component I used Ember's built in ApplicationController for simplicity.
notifyPropertyChange():This is called because when we are inserting an new string into the selected array, using the push functionality of arrays.
I have used the push method because this is the most efficient way to add a new entry into an existing array.
While Ember does have a pushObject method that is supposed to take care of the notification as well, I couldn't get it to honour this. So this.notifyPropertyChange("selected"); tells Ember that we updated the array. However I'm hoping that's not a dealbreaker.
If you don't wish to use it in Component format, you could implement it as a view. It ultimately achieves the same goal, but this may be a more familiar design pattern to you.
See this JSBin for implementation as a View. I won't include the full code here, because some of it is the same as above, you can see it in the JSBin
Create an instance of App.SelectFilterBoxView, with a controller that has a data and selected property:
var myView = App.SelectFilterBoxView.create({
controller: Ember.Object.create({
data: DATA.model_data,
selected: ['Author','']
})
});
Then append the view as required, such as to #main.
myView.appendTo("#main");
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