I'm very new to AngularJS and MVVM in general and was looking for the best way to deal with displaying a model that also needs to display a couple of fields from child model objects on the web UI.
At the moment following basic tutorials my model object in my AngularJS controller reflects exactly my Rails model, and so I can't access fields from my child objects and just see their IDs from the foreign key columns in the database.
I'm wondering what the best convention is for dealing with this situation?
do I create a tableless model in Rails that contains only the fields needed by the presentation layer. Me defining what the presentation layer needs in Rails seems like it defeats the point of using MVVM.
do I create something on the AngularJS side that queries for the child objects using those exposed foreign key IDs? If so, how do I optimise it to avoid performing a request for each of my 50 objects in the table.
Yeah! You should define your api to contain all the data needed for a request. You don't need to create a tabless model for that.
If for example a fetch the json for a Post, Author and Comments json representation also should be there, or at least some part of it.
You might want to take a look at https://github.com/rails-api/active_model_serializers or https://github.com/nesquena/rabl
Related
If I create models for request and response parameters for every http request in iOS project, it is easier for me to deal with models rather than dictionaries.
However, it will create too many models.
Is this a good approach or not?
And during the development, I found if there is only one model, for example, in an online shopping system, I only have one store model. But I use it in store module, cart model and order model. Actually in each module, the different attributes of the store model has been used. So this giant model always has some extra attributes for usage in each module.
Is this a good approach to manage the models in iOS projects? Or should I create CartStore model, OrderStore model?
To me, you should create models for different flows/modules to adapt Single Responsibility Principle.
From your shoes, the Store model should only contain the attributes of the store, if Cart or Order module need any further attributes then you should create another model.
Hope this helps.
The model approach will save a ton of your time when come back to fix or add on a new feature. Sure, They will take quite time but today Apple has already provide code codable/decodable protocol which will help you to handle parsing between JSON and Object Model. Also writing a unit test or even integration test it will be much easier for you.
Base on which data response of request, if have the same data structure should only create 1.
Ex: api get all stores and api get store with condition (distance, rating, ...) return storeModel, then we just using only 1 storeModel. And we have api get store detail (this api return more info than api get list stores above) just add more property in storeModel and using it again. So that with 3 apis, we only using storeModel
With your example, I think should create StoreModel, CartModel and OrderModel inherits from BaseModel. In this BaseModel, we'll have the all property which StoreModel, CartModel and OrderModel have, and in each children model, we will have only specific property.
Hope this help!
What is the best approach for maintaining (CRUD) on an optiongroup list that is driven by two sql server tables?
The option group is like this and is driven simply by two tables (parent child)
OptionGroupOne
ItemOne
ItemTwo
OptionGroupTwo
SecondItemOne
SecondItemTwo
etc…………….
Was thinking of just looping through in an unordered list?
I’m using entity framework 6 with MVC5 don't really want to use javascript.
This is a long way if you don't seem to have anything ready yet... I bet that's the reason why no one wants to start explaining.
You should organise the Lists in nested ViewModels, the OptionGroupViewModel and the ItemViewModel. The OptionGroupViewModel has a string property for the name and a List<ItemViewModel> property for the children. So the main model should be a List<OptionGroupViewModel>.
In your cshtml, Using the Html.EditorForModel() extension method on a the latter, you should get some View Results already, the EditorFor... methods are quite intelligent and will generate views based on the data structure.
Now you will need a MVC Post method with the List as the model and you will find all updates there, You need to map them back to the Entity Framework model (or whatever kind of base model you have). As you mentioned in your comment above, you want just a "way of editing the titles of each option group and the title of each group". This would be pretty simple but is half way to CRUD, and Delete + Add are much trickier in that scenario.
Using frameworks like Knockout JS is a big gain here but requires some learning and will introduce JavaScript to your project. The linked tutorial is for Web.Api but it will also work for MVC.
I'm starting to use Redis, and first thing my code is not too DRY, and was going to consolidate it in the application.rb and controller. Is this the best way to go, or should I make a new Class called Redis, and have all the logic in there?
My models are currently Customers, Orders, Products, and I'm using a lot of counters.
You will probably need a combination of new and existing model classes.
In many cases you can just drop the model used by the view directly into the datastore, which saves repetition. However, there will always be some places where the needs of the view and the datastore are different.
For example a property that appears as a list of values in the view may need to be stored as a separate set key rather than serialized with the other properties of the model.
This is possibly a bit of a stupid question, but I am getting confused due to the ASP.NET MVC book I am currently reading...
Working with Linq-To-SQL it seems to say that it is not good practice to pass the Linq-to-SQL objects straight to the controller, but that each object should be modelled separately first and this should be passed between the controller and the repository.
Say, I have a database of products. Linq-to-SQl creates a product class for me with Name, Price and Whatnotelse properties. I could pass that straight from repository to controller and then view, but instead it seems to recommend that I use and third class, say Product_Entity, with also Name, Price etc. properties and pass that to the controller.
I fail to see the benefit of this approach, except possibly for adding attributes to the properties... But apart from that it seems to have more drawbacks than benefits. Say each product has manufacturer information as well, I don't see how I can model that easily in my third class.
Is this approach really best practice? Or did I misunderstand all that? If so, why is it bad to work straight off the linq-to-sql generated objects? And how do you deal with relationships between objects in y
The huge benefit to this other class you create is that, to use your example, it doesn't necessarily map to either a product or a manufacturer. Think about it like this:
Your Linq to SQL classes are meant for talking in the "data" domain.
Your "data" classes (the ones you're having trouble with) are meant for talking in the "application" domain.
Let's take an example. Suppose in your MVC application you wanted to show a grid of information about products. You want to see their Name, Price (from the Product table) and their Country of Manufacture and Manufacturer name (from the Manufacturer table). What would you name this class? Product_Manufacturer? What if later on you wanted to add properties from yet a third table such as product discounts? Instead of thinking about these objects in purely the data domain, think about them with regard to your application.
So instead of Product_Manufacturer, what about calling it ProductSummaryItem? Each property of the ProductSummaryItem class would map 1:1 with a field shown in your grid on the UI. Your controller would perform the mapping between the information in the data domain (Product, Manufacturer) with the custom class you'd created in the application domain (ProductSummaryItem).
By doing this, you get some awesome benefits:
1) Writing your views becomes really, really simple. All you have to do to display your data is loop through the ProductSummaryItems and wrap them in and tags, and you're done. It also allows for simple aggregation. Say for example you wanted to add a field called ProductsSoldLastYear to your ProductSummaryItem class. You could do that very simply in your views because all it is to them is another property.
2) Since the view is trivial and there's mapping logic in the controller, it becomes much easier to test the controller's output because it's customized to what the view is going to see.
3) Since the ProductSummaryItem class only has the data it needs, your queries can potentially become much faster because they only need to query for the fields that would populate your ProductSummaryItem object, and nothing else. This overhead can become overbearing the more data-domain objects make up your ProductSummaryItem object.
This pattern is called Model View ViewModel (MVVM) and is hugely popular with MVC as well as in frameworks like WPF.
The argument against MVVM is that you have to somewhat reimplement simple classes for CRUD operations. Fair enough, I guess, but you can use a tool like automapper to help out with things like that. I think you'll find fairly quickly, though, that using the MVVM pattern even for CRUD pays dividends, because before you know it, even with simple classes, you'll start wishing you had extra fields which can easily drive your views.
I am having trouble understanding ORM in Ruby on Rails. From what I understand there is a 1:1 relationship between tables/columns and objects/attributes. So every record is an object.
Also what exactly is a Model? I know it maps to a table.
What I'm really after is a deeper understanding of the above. Thank you in advance for your help
I'm a Web developer going from PHP to Ruby on Rails.
"From what I understand there is a 1:1 relationship between tables/columns and objects/attributes. So every record is an object."
That is not exactly correct, unless you use the term "object" very loosely. Tables are modelled by classes, while table records are modeled by instances of those classes.
Let's say you have a clients table, with columns id (autonum) and name (varchar). Let's say that it has only one record, id=1 and a name="Ford". Then:
The DB table clients will map to the model class Client.
The record will map to a model instance, meaning that you have to create the object and assign it to a variable in order to work with the record. The most common way would be to do ford = Client.find(1)
The two columns of the table will map to methods on the ford variable. You can do ford.id and you will get 1. You can do ford.name and you will get the string "Ford". You can also change the name of the client by doing ford.name = "Chevrolet", and then commit the changes on the database by doing ford.save.
"Also what exactly is a Model? I know it maps to a table"
Models are just classes with lots of very useful methods for manipulating your database. Here are some examples:
Validations: Besides the typical db-driven validations ("this field can't be null") you can implement much complex validations in ruby ("this field must be a valid email" is the most typical one). Validations are run just before you invoke "save" on a model instance.
Relationships: The foreign keys can also be mapped onto models. For example, if you had a brands table (with its corresponding Brand model) associated via a foreign key to your ford client, you could do ford.brands and you would get an array of objects representing all the records on the brands table that have a client_id = 1.
Queries: Models allow you to create queries in ruby, and translate them to SQL themselves. Most people like this feature.
These are just some examples. Active record provides much more functionalities such as translations, scoping in queries, or support for single table inheritance.
Last but not least, you can add your own methods to these classes.
Models are a great way of not writing "spaguetti code", since you are kind of forced to separate your code by functionality.
Models handle database interaction, and business logic
Views handle html rendering and user interaction
Controllers connect Models with Views
ORM in Rails is an implementation of the Active Record pattern from Martin Fowler's Patterns of Enterprise Application Architecture book. Accordingly, the Rails ORM framework is named ActiveRecord.
The basic idea is that a database table is wrapped into a class and an instance of an object corresponds to a single row in that table. So creating a new instance adds a row to the table, updating the object updates the row etc. The wrapper class implements properties for each column in the table. In Rails' ActiveRecord, these properties are made available automatically using Ruby metaprogramming based on the database schema. You can override these properties if required if you need to introduce additional logic. You can also add so-called virtual attributes, which have no corresponding column in the underlying database table.
Rails is a Model-View-Controller (MVC) framework, so a Rails model is the M in MVC. As well as being the ActiveRecord wrapper class described above it contains business logic, including validation logic implemented by ActiveRecord's Validation module.
Further Reading
Rails Database Migrations guide
Rails Active Record Validations and Callbacks guide
Active Record Associations guide
Active Record Query Interface guide
Active Record API documentation
Models: Domain objects such like User, Account or Status. Models are not necessarily supported by a database backend, as for example Status can be just a simple statically-typed enumeration.
ActiveRecord:
Provides dynamic methods for quering database tables. A database table is defined as a class which inherits ActiveRecord class (pseudo-PHP example):
class User extends ActiveRecord {}
//find a record by name, and returns an instance of `User`
$record = User::find_by_name("Imran");
echo $record->name; //prints "Imran"
//there are a lot more dynamic methods for quering
New records are created by creating new instances of ActiveRecord-inherited classes:
class Account extends ActiveRecord {}
$account = new Account();
$account->name = "Bank Account";
$account->save();
There are two pieces here: the ORM and Rails's MVC pattern. ORM is short for "object-relational mapping", and it does pretty much what it says: it maps tables in your database to objects you can work with.
MVC is short for "model-view-controller", the pattern that describes how Rails turns your domain behavior and object representations into useful pages. The MVC pattern breaks down into three chunks:
Models contain a definition of what an object in your domain represents, and how it is related to other models. It also describes how fields and relationships represented in the object map to backing stores (such as a database). Note that, per se, there's nothing about a model which prescribes that you have to use a particular ORM (or even an ORM at all).
Controllers specify how models should interact with each other to produce useful results in response to a user request.
Views take the results created by controllers and render them in the desired way. (By the time you get to your view, you should mostly know what's being rendered, and there should be very little behavior happening.)
The definition from Wikipedia:
Object-relational mapping (ORM, O/RM,
and O/R mapping) in computer software
is a programming technique for
converting data between incompatible
type systems in relational databases
and object-oriented programming
languages. This creates, in effect, a
"virtual object database" that can be
used from within the programming
language.
From a PHP view it will be in the following way(via example)
Connect to the database and get some row from posts table.
Turn that row to an object with attributes like those in the table columns.
If the posts has comments in comments table, you can also do post.comments and you get the comments also as an array of objects as well.
You can define relationships between tables like saying: Posts has_many Comments, a Comment belongs to a post and so.
So basically you are not working with database rows, instead you turn those rows and their relationships to objects with composition or inheritance relationships.
In layman's terms.
A Rails Model is proxy to a table in the database. These models happens to be Ruby classes.
The objects of these classes are proxies to rows in the table of which this model is a proxy.
Finally the attributes of these objects are proxies to the column data for that particular row.
Above is actually the Rails ActiveRecord ORM.
1:1 is not quite correct, since there is object-relation impedance mismatch.