Below is a common pattern in RESTful design:
GET /entities/{entity_id} # fetch single entity
GET /entities/ # list all the entities
however if users have a bug where entity ID is accidentally set to "" (not uncommon), then that will result in a 200 status (instead of a 400).
Wouldn't GET /entities/list be more user friendly? or GET /entity/{entity_id} + /entities
Related
In spring data neo4j I have simple one-to-many relationship: (:User)-[:EMPLOYEE_OF]->(:Company). User can be employee of only one company. Here are my entities:
class User(#Relationship(type = "EMPLOYEE_OF") var company: Company? = null, /* ids etc */)
class Company(/* ids etc */)
When I want to change target of that relationship or remove it neo4j keeps adding new relationships instead of replacing it.
val user = userRepository.findByName("user1")
val company = companyRepository.findByName("company1")
user.company = company
userRepository.save(user)
// 2nd case
user.company = null
userRepository.save(user)
In both cases, relationships are only added, never removed.
Is there a proper way to do it?
You have to put the load / find and the save in a transaction. The best way in a Spring project to do this is to extract the logic into a service layer method of your application and mark it as #Transactional.
Within this transaction, Spring Data Neo4j / Neo4j-OGM can track the changes that happen on the node and change or remove the relationships.
I want to support pagination in my RESTful API.
My API method should return a JSON list of product via http://localhost/products/v1/getproductsbycategory, there are potentially thousands of products, and I want to page through them, so my request should look something like this:
public function getProductsByCategory($product_id,$page){
$perPage=5;
$start=($page-1)*$perPage;
$stmt=$this->conn->prepare("SELECT id,product,description,destination_url,expiry_type,savings,expiry,title,last_updated_on FROM products WHERE product_id=? ORDER BY last_updted_on DESC LIMIT $start ,$perPage");
$stmt->bind_param('i',$category_id);
$stmt->execute();
$productbycategory=$stmt->get_result();
$stmt->close();
return $productbycategory;
}
}
Firstly, in a RESTful call, the URL should ideally be noun-based and not verbs. We are using HTTP verbs (GET, PUT, POST, etc) to do an action on a noun - product in your case.
So, the URL should be http://localhost/products/v1/category
This effectively means you are GETting product of type v1 based on category. To get a given page number, simply add it as a query parameter -
http://localhost/products/v1/category?page=1
and handle it accordingly in your GET implementation corresponding to localhost/products/v1/category
Hope this helps.
Pagination has nothing to do with the JSON format per se - it's all about the query string in the URL and how the server interprets that.
Expanding on #Sampada's answer, you can have a URL like
http://localhost/products/v1/category?pageSize=5&pageNumber=2
and then you'll simply pick the corresponding elements on the server side (consider whether you'll want 0 or 1-based index for the pageNumber), and return them.
Additionally you can wrap this collection in an object that also provides links as to navigate to the previous/next/specific page - see HATEOAS & Richardson's Maturity Model level 3.
I'm using the AR includes method to execute a LEFT OUTER JOIN between objects User and Building, where a User may or may not have a Building association:
users = User.includes(:building).references(:buildings)
Since I'm using references, any associated Building objects will be eager loaded.
My expectation was that I would then be able to iterate through the list of users, and check whether a user had a building associated with them without triggering additional queries, but I see that in fact whenever I try to access the building property of a user that doesn't have one, AR makes another SQL call to try and retrieve that building (though on subsequent tries it will just return nil).
These queries are obviously redundant as the association would have been loaded during the initial join, and seems to defeat the whole purpose of eager loading with includes/references, as now I'm looking at N times the number of queries equal to the number of empty associations.
users.each do | user |
# This will trigger a new query when building is not present:
# SELECT "buildings".* FROM "buildings" WHERE "buildings"."address" = $1 LIMIT 1 [["address", "123 my street"]]
if user.building
puts 'User has building'
else
puts 'User has no building'
end
end
User class:
class User < ActiveRecord::Base
belongs_to :building, foreign_key: 'residence_id'
end
Is there a way to check the presence of the users' building association without triggering extra queries?
ON RAILS 4.2.0 / POSTGRES
UPDATE:
Thank you #BoraMa for putting together this test. Looks like we're getting different behavior across recent Rails versions:
OUTPUT (RAILS 4.2.0):
User 1 has building
User 2 has building
User 3 has no building
D, [2016-05-26T11:48:38.147316 #11910] DEBUG -- : Building Load (0.2ms) SELECT "buildings".* FROM "buildings" WHERE "buildings"."id" = $1 LIMIT 1 [["id", 123]]
User 4 has no building
OUTPUT (RAILS 4.2.6)
User 1 has building
User 2 has building
User 3 has no building
User 4 has no building
OUTPUT (RAILS 5.0.0)
User 1 has building
User 2 has building
User 3 has no building
User 4 has no building
Take aways:
This issue was limited to "dangling foreign keys (ie the residence_id
column is not nil but there is no corresponding building object)"
(THANKS #FrederickCheung)
The issue has been resolved as of Rails 4.2.6
Sounds like you got bit by a bug in Active Record, that was fixed in rails 4.2.3.
In the case where the column was nil Active Record already knows that it doesn't even need to try loading the associated object. The remaining cases were the ones impacted by this bug
Seems like a typo, please notice building instead of buildings: User.includes(:building).references(:buildings)
That should trigger the big query that uses the format of AS tX_rY for each association and table.
It seems that since rails 4.1 there are potential clashes with how just how implicit #includes should be, see the following open issue.
This code is all untested for syntax, but there would be two approaches I would try:
1/ Make the eager loading implicit
users = User.eager_load(:building).preload(:buildings)
2/ Separate out the two types of users, ones where the building is attached, meaning you don't even try and preload the building, removing the innefficiency.
users = User.includes(:building).where.not(residence_id: nil).references(:buildings)
users.each do | user|
puts "User has building: #{user} #{user.building}"
end
# No additional references needed to be eager-loaded.
users = User.where(residence_id: nil)
users.each do | user |
puts "#{User} has no building."
end
Question
How do I return different results for the same resource?
Details
I have been searching for some time now about the proper way to build a RESTful API. Tons of great information out there. Now I am actually trying to apply this to my website and have run into a few snags. I found a few suggestions that said to base the resources on your database as a starting point, considering your database should be structured decently. Here is my scenario:
My Site:
Here is a little information about my website and the purpose of the API
We are creating a site that allows people to play games. The API is supposed to allow other developers to build their own games and use our backend to collect user information and store it.
Scenario 1:
We have a players database that stores all player data. A developer needs to select this data based on either a user_id (person who owns the player data) or a game_id (the game that collected the data).
Resource
http://site.com/api/players
Issue:
If the developer calls my resource using GET they will receive a list of players. Since there are multiple developers using this system they must specify some ID by which to select all the players. This is where I find a problem. I want the developer to be able to specify two kinds of ID's. They can select all players by user_id or by game_id.
How do you handle this?
Do I need two separate resources?
Lets say you have a controller name 'Players', then you'll have 2 methods:
function user_get(){
//get id from request and do something
}
function game_get(){
//get id from request and do something
}
now the url will look like: http://site.com/api/players/user/333, http://site.com/api/players/game/333
player is the controller.
user/game are the action
If you use phil sturgeon's framework, you'll do that but the url will look like:
http://site.com/api/players/user/id/333, http://site.com/api/players/game/id/333
and then you get the id using : $this->get('id');
You can limit the results by specifying querystring parameters, i.e:
http://site.com/api/players?id=123
http://site.com/api/players?name=Paolo
use phil's REST Server library: https://github.com/philsturgeon/codeigniter-restserver
I use this library in a product environment using oauth, and api key generation. You would create a api controller, and define methods for each of the requests you want. In my case i created an entirely seperate codeigniter instance and just wrote my models as i needed them.
You can also use this REST library to insert data, its all in his documentation..
Here is a video Phil threw together on the basics back in 2011..
http://philsturgeon.co.uk/blog/2011/03/video-set-up-a-rest-api-with-codeigniter
It should go noted, that RESTful URLs mean using plural/singular wording e.g; player = singular, players = all or more than one, games|game etc..
this will allow you to do things like this in your controller
//users method_get is the http req type.. you could use post, or put as well.
public function players_get(){
//query db for players, pass back data
}
Your API Request URL would be something like:
http://api.example.com/players/format/[csv|json|xml|html|php]
this would return a json object of all the users based on your query in your model.
OR
public function player_get($id = false, $game = false){
//if $game_id isset, search by game_id
//query db for a specific player, pass back data
}
Your API Request URL would be something like:
http://api.example.com/player/game/1/format/[csv|json|xml|html|php]
OR
public function playerGames_get($id){
//query db for a specific players games based on $userid
}
Your API Request URL would be something like:
http://api.example.com/playerGames/1/format/[csv|json|xml|html|php]
I would like to return a DTO from my data layer which would also contain child collections...such as this:
Audio
- Title
- Description
- Filename
- Tags
- TagName
- Comments
- PersonName
- CommentText
Here is a basic query so far, but i'm not sure how to transform the child collections from my entity to the DTO.
var query = Session.CreateCriteria<Audio>("audio")
.SetProjection(
Projections.ProjectionList()
.Add(Projections.Property<Audio>(x => x.Title))
.Add(Projections.Property<Audio>(x => x.Description))
.Add(Projections.Property<Audio>(x => x.Filename))
).SetResultTransformer(new AliasToBeanResultTransformer(typeof(AudioDto)))
.List<AudioDto>();
Is this even possible, or is there another reccomended way of doing this?
UPDATE:
Just want to add a little more information about my scenario...I want to return a list of Audio items to the currently logged in user along with some associated entities such as tags, comments etc...these are fairly straight forward using MultiQuery / Future.
However, when displaying the audio items to the user, i also want to display 3 other options to the user:
Weather they have added this audio item to their list of favourites
Weather they have given this audio the 'thumbs up'
Weather the logged in user is 'Following' the owner of this audio
Favourites : Audio -> HasMany -> AudioUserFavourites
Thumbs Up : Audio -> HasManyToMany -> UserAccount
Following Owner : Audio -> References -> UserAccount ->
ManyToMany -> UserAccount
Hope this makes sense...if not i'll try and explain again...how can I eager load these extra details for each Audio entity returned...I need all this information in pages of 20 also.
I looked at Batch fetching, but this appears to fetch ALL thumbs ups for each Audio entity, rather than checking if only the logged in user has thumbed it.
Sorry for rambling :-)
Paul
If you want to fetch your Audio objects with both the Tags collection and Comments collections populated, have a look at Aydende Rahien's blog: http://ayende.com/blog/4367/eagerly-loading-entity-associations-efficiently-with-nhibernate.
You don't need to use DTOs for this; you can get back a list of Audio with its collections even if the collections are lazily loaded by default. You would create two future queries; the first will fetch Audio joined to Tags, and the second will fetch Audio joined to Comments. It works because by the time the second query result is being processed, the session cache already has the Audio objects in it; NHibernate grabs the Audio from the cache instead of rehydrating it, and then fills in the second collection.
You don't need to use future queries for this; it still works if you just execute the two queries sequentially, but using futures will result in just one round trip to the database, making it faster.