feat(select,ng-options): New expression (identify by) in ng-options

[quazzie]

Add a new expression (identify by) in ng-options.
This can be used when working with objects. Instead of objects comparing by reference
it will compare by ex. a property.

So you can write:

ng-options="obj identify by obj.id as obj.name for obj in objects"

The identify part will be used when checking for equality of objects.

Example:
If you get an json object from server with nested objects and a collection of those nested
objects you can use this to select correct object.

<select
    ng-model="user.building"
    ng-options="building identify by building.id as building.name 
                      for building in buildings"
    >
</select>

//scope.user comes as json from server
//scope.buildings comes as jsonarray from server
scope: {
  user: { 
      name: 'Test user', 
      building: { id: 1, name: 'Office 1', address: 'Bla bla 12', rooms: 4 } 
  }
  buildings: [
    { id: 1, name: 'Office 1', address: 'Bla bla 12', rooms: 4 }, 
    { id: 2, name: 'Office 2', address: 'Bla bla 13', rooms: 5 },
    ... 
  ]
}

This will correctly select building with id 1 in the select and when select is changed
it will populate the user with the building object selected.

[icenine457]

This would be a godsend for my application, as I'm using Mongo and having to do an additional look-up based on an identifier seems sloppy.

FYI: Knockout has similar capabilities by setting optionText and optionValue bindings. Works like a charm.

PS: I was impatient, and so I cloned your branch and am using this now (not in a production environment, but I'm really hopeful this makes it in!)

[pavelarnost]

This patch (or some alternative of it) should definitely be accepted. Without it, a lot of unnecessary boilerplate code is needed.

[nils-wisiol]

Is this patch likely to be merged? It would be a great help for me, too.

[g00fy-]

+1, why this patch isn't accepted or closed yet?

[petebacondarwin]

It ought to be using a syntax similar, or compatible to, the new ng-repeat syntax: Master Repeat Docs

[g00fy-]

@petebacondarwin do you mean variable in expression track by tracking_expression ?

[quazzie]

Sure, i'm not picky on syntax. I'll take a look at changing it tomorrow.

[quazzie]

Uhmm should it be
"select item as item.text track by item.id for item in items" or
"select item track by item.id as item.text for item in items" ?

[petebacondarwin]

Whatever it is we should try to maintain some level of consistency across the various comprehension syntaxes. This track keyword seems unnecessary to me, but there you go. My take on the ng-options syntax would be:

ng-options="item as item.text for item in items track by item.id"

But again we need someone in the core team to chime in here.

[quazzie]

I agree that we need some input from core team.

[IgorMinar]

+1 for @petebacondarwin's syntax. let's go forward with that.

[quazzie]

Was it this correct to add a commit ?
Sorry, i'm still learning git.

[quazzie]

Uhmm it looks like it got merged with my other patch (backbutton-locationchangestart)...
And i have no idea why...

[quazzie]

Think i fixed it... ? :)

[petebacondarwin]

PR Checklist (Minor Feature)

• Contributor signed CLA now or in the past (if you just signed, leave a comment here with your real name for cross reference)
• Feature improves existing core functionality
• API is compatible with existing Angular apis and relevant standards (if applicable)
• PR doesn't contain a breaking change
• PR contains unit tests
• PR contains e2e tests (if suitable)
• PR contains documentation update
• PR passes all tests on Travis (sanity)
• PR passes all tests on ci.angularjs.org (cross-browser compatibility)
• PR is rebased against recent master
• PR is squashed into one commit per logical change
• PR's commit messages are descriptive and allows us to autogenerate release notes (required commit message format)
• All changes requested in review have been implemented

[petebacondarwin]

Landed at: c32a859. Thanks!