Given the following prisma model:
model User {
user_id String #id #default(uuid())
groups Group[] #relation("CreatedGroups")
participating_groups Group[] #relation("Participants") // -- keep track!
}
model Group {
group_id String #id #default(uuid())
participants User[] #relation("Participants") // -- keep track too!
creator_id String
creator User #relation("CreatedGroups", fields: [creator_id], references: [user_id])
}
Say i needed to add one participant into a group. By doing so, i'm updating 2 things:
The participants array in the Group model. (connecting the user)
The participating_groups array in the User model. (connecting the group)
Notice i've set a #relation at each field to mention it's related opposite at the other model.
My question is, how do i implement that in one single query, instead of updating both models seperately?
Related
I have a table that describes a document with title, content, created_at, etc and a struct that describes columns to filter that table
struct Partial {
handle: String,
title: String,
content: String,
created_at: DateTime<Utc>,
updated_at: DateTime<Utc>,
}
which; after some transformations, I pass to the database layer and depending on who the user is, return a set of rows.
For example, if user is the author, user can search any columns, otherwise they can search only publicly visible documents.
A user can also 'share' a document with another user so if there a share from the requester to the document owner, the user should also be able to search in those documents as well.
There are two ways to go about that (as far as I know)
Use inner joins and filter on columns
INNER JOIN author on document.id = author.document_id
INNER JOIN visibility on document.id = visibility.document_id
INNER JOIN share on document.id = share.document_id
...
...
...
WHERE document.handle = $handle -- from `Partial` struct
WHERE document.title = $title -- from `Partial` struct
WHERE document.content = $content -- from `Partial` struct
WHERE author.user_id = $user_id -- from user info passed to db
WHERE visibility.scope = 'PUBLIC' -- from user info passed to db
WHERE share.shared_to = $user_id -- from user info passed to db
WHERE group.member = $user_id -- from user info passed to db
...
...
...
This requires passing user information ($user_id for this example but this also sometimes includes additional info like if the user is blocked or the account is non-public, belongs to a group, etc. Around 12 properties in total) to the database layer.
generate a list of ids in application layer and pass it on to the database layer.
For example,
let public_document_ids = visibility.find(Find { visibility: Visibility::Public }).map(|visibility_row| visibility_row.document_id).collect();
let authored_document_ids = author.find(Find { document_author: user_id }).map(|authored_row| authored_row.document_id).collect();
let shared_document_ids = share.find(Find { shared_to: user_id }).map(|share_row| share_row.document_id).collect();
and then pass sum of all of these ids to database
WHERE document.handle = $handle -- from `Partial` struct
WHERE document.title = $title -- from `Partial` struct
WHERE document.content = $content -- from `Partial` struct
WHERE document.id IN $ids -- from `ids` passed to db
...
...
...
To me it seems that the first approach of using inner joins and filtering on columns in the database can
potentially be more efficient,
and a lot more easier to get right
but the second approach, generating a list of ids in the application layer, allows
a lot more flexibility and
also lets me use different (distributed) databases to store different tables (perhaps even different database drivers)
It also reduces the amount of user information passed to the database layer
but it also requires loading all the data into the application layer before filtering the results
and implementing pagination will be lot more complex
So my question - is there a way to know which approach I should go with? Perhaps there's something I haven't considered yet.
I have two tables:
dbo.Dashboards
Id (int PK) Title(nvarchar) WidgetIds(nvarchar)
1 Test [1,2]
dbo.Widgets
Id (int PK) Details(nvarchar)
1 {'text': 'some data'}
2 {'text': 'test'}
Expected output:
Dashboard.Id Dashboard.Title Widget.Id Widget.Details
1 Test 1 {'text': 'some data'}
1 Test 2 {'text': 'test'}
I would like to get dashboards with assigned widgets by using Entity Framework.
My first solution is to get dbo.Dashboards and then dbo.Widgets. After that I can merge it in a backend, but it is not the best practice.
Is there any option to get Dashboards with assigned Widget list?
Function Include() is not working because there isn't FK relationship between tables.
It seems to me that you have a many-to-many relationship between Dashboards and Widgets: Every Dashboard has zero or more Widgets and every Widget is used by zero or more Dashboards.
In a proper database you would have a separate junction table. Apparently you chose not to use this pattern, but create a string that contains a textual representation of the widgets that a 'Dashboard` has.
If you plan to create a serious application I strongly advise you to
use the standard pattern in many-to-many relationships
If you don't, all your queries will be more difficult. Imagine the problems you'll experience if you want to delete a Widget. You'd have to check the textual representation of every Dashboard to check if the widget that you want to remove is used somewhere and change it.
If you want to configure your many-to-many relations ship according to the Entity Framework Code-First Conventions, you will have something like this:
class Dashboard
{
public int Id {get; set;}
public string Title {get; set;}
// every Dashboard has zero or more Widgets
public virtual ICollection<Widget> Widgets {get; set;}
... // other properties
}
class Widget
{
public int Id {get; set;}
// every Widget is used in zero or more Dashboards
public virtual ICollection<Dashboard> Dashboards{get; set;}
... // other widget properties
}
class MyDbContext : DbContext
{
public DbSet<Dashboard> Dashboards {get; set;}
public DbSet<Widget> Widgets {get; set;}
}
Because you stuck to the conventions, this is all that entity framework needs to know to understand that you want to configure a many-to-many relationship between Dashboards and Widgets. Entity Framework will create the junction table for you. It will automatically update this table whenever you add a Widget to a Dashboard. It will also create the proper joins whenever you want to fetch Dashboards with their Widgets, or Widgets with the Dasheboards that use them.
Your query will be fairly simple:
var DashBoardsWithTheirWidgets = myDbcontext.Dashboards
// I only want to see the super dashboards
.Where(dashboard => dashboard.Type = DashboardType.Super)
.Select(dashboard => new
{
// Select only the properties you plan to use:
Id = dashboard.Id,
Title = dashboard.Title,
// select only the Widgets you plan to use:
Widgets = dashboard.Widgets
.Where(widget => widget.Price > 100.00)
.Select(widget => new
{
// again select only the properties you plan to use
Name = widget.Name,
Price = widget.Price,
})
.ToList();
});
See how easy it is if you stick to the conventions?
If you really want your obscure method of using foreign keys, you need a function to remove the square brackets and the commas from the widgetIds, split the string into sub-strings, Parse them to numbers, and do a join.
But before you plan to continue on this path, experiment on how to add a Widget and a Dashboard. How to add a Widget to a Dashboard, how to remove a Widget. I think the time needed to reform your database into proper format is much less than the time you'll need to implement those functions
Solution 1:
You need to restructure the dbo.dashboards table. Change the column layout of dbo.dashboards to
Auto_Generated_ID, Unique_Identifier(PK), Title, WidgetIds
I know the above column restructuring is done in a bad way. But still this will work in your case.
After redesigning it you can use join between dbo.dashboards and dbo.widgets to retrieve it in an efficient way.
Solution 2:
The below-normalized tables will work in your case
dbo.dashboard
id, title (columns)
dbo.dashboard_widget
id, dashboard_id, widget_id (columns)
dbo.widgets
id, details (columns)
Query:
select d.id, d.title, dw.widget_ids, w. details from dbo.dashboard d INNER JOIN dbo.dashboard_widget dw ON d.id = dw.dashboard_id INNER JOIN dbo.widgets w ON dw.widget_id = w.id where d.id = << id number >>
I'm following the core ef-mvc tutorial (https://learn.microsoft.com/en-us/aspnet/core/data/ef-mvc/complex-data-model) and I have a two models that share a many-to-many relationship with each other, which means that I have to have a one-to-many relationship defined between both these classes and a class that's used exclusively for the join table, right? ie.
public class JoinTable
{
public int model1ID;
public model1 model1;
public int model2ID;
public model2 model2;
}
In the example DbInitializer seed method, this code:
foreach(Enrollment e in enrollments)
{
var enrollmentInDataBase = context.Enrollments.Where(
s =>
s.Student.ID == e.StudentID &&
s.Course.CourseID == e.CourseID).SingleOrDefault();
if (enrollmentInDataBase == null)
{
context.Enrollments.Add(e);
}
}
Essentially saves all entities defined in the seed method that don't already exist in the table. How could I write a method that will save the entity to the database up to x amount of times (I need this capability for my own app)? Also based on my knowledge, I'm certain that there is an implicit restriction in the data model (or table) definition that would have to be altered?
Answered in comments, but moving here for visibility:
You want to have a third property in DeckCard called Count with only 1 entry for each card and the count will be how many of that card is in the Deck.
I have a User, Role & Page setup, all with many-to-many relationships and the pivot tables setup in the usual fashion (role_user, page_role), along with the eloquent methods to attach a model to the pivot tables.
My idea is to allow a user to have many roles, and a page can be accessed by many roles.
However now I'd like to return a collection where I have my users details and then the pages they're allowed to access.
The closest I have got is:
return User::find( Auth::user()->id )->with('roles.pages')->first()->roles;
Now this returns each role the user has, and each page that the role can access. Which is correct, however I have duplication on the pages part.
How would I go about getting only a list of pages the user is able to access with no duplication?
Cheers
Read that answer to get you on the track: HasManyThrough with one-to-many relationship
Only for your setup you need to adjust the query - join 2 pivot tables (and make sure they represent real data, ie no rows referencing non-existing models):
// User model
// accessor so you can access it like any relation: $user->pages;
public function getPagesAttribute()
{
if ( ! array_key_exists('pages', $this->relations)) $this->loadPages();
return $this->getRelation('pages');
}
// here you load the pages and set the collection as a relation
protected function loadPages()
{
$pages = Page::join('page_role as pr', 'pr.page_id', '=', 'pages.id')
->join('role_user as ru', 'ru.role_id', '=', 'pr.role_id')
->where('ru.user_id', $this->id)
->distinct()
->get(['pages.*', 'user_id']);
$hasMany = new Illuminate\Database\Eloquent\Relations\HasMany(Page::query(), $this, 'user_id', 'id');
$hasMany->matchMany(array($this), $pages, 'pages');
return $this;
}
One more thing: I hardcoded tables and columns names for sake of simplicity, but in real life I suggest you rely on the relationships and their getters, like: $relation->getTable(), $relation->getForeignKey() etc.
Now suggestion about your code:
return User::find( // 2. query to get the same user
Auth::user()->id // 1. query to get the user and his id
)->with('roles.pages')
->first() // 3. query to get ANOTHER user (or the same, luckily..)
->roles;
Use Auth::id() instead of Auth::user()->id (for Laravel ver 4.1.25+) to avoid redundant query
find() and first() are methods that execute the query, so you just returned the user with id = Auth::user()->id and moment later you fetch another one, who comes first() from the users table..
You don't need to use User::whatever for authenticated user, use Auth::user() instead.
So the code with suggested solution would look like this:
Auth::user()->pages; // collection of Page models with unique entries
I have 3 related objects (Entry, GamePlay, Prize) and I'm trying to find the best way to query them for what I need using NHibernate. When a request comes in, I need to query the Entries table for a matching entry and, if found, get a) the latest game play along with the first game play that has a prize attached. Prize is a child of GamePlay and each Entry object has a GamePlays property (IList).
Currently, I'm working on a method that pulls the matching Entry and eagerly loads all game plays and associated prizes, but it seems wasteful to load all game plays just to find the latest one and any that contain a prize.
Right now, my query looks like this:
var entry = session.CreateCriteria<Entry>()
.Add(Restrictions.Eq("Phone", phone))
.AddOrder(Order.Desc("Created"))
.SetFetchMode("GamePlays", FetchMode.Join)
.SetMaxResults(1).UniqueResult<Entry>();
Two problems with this:
It loads all game plays up front. With 365 days of data, this could easily balloon to 300k of data per query.
It doesn't eagerly load the Prize child property for each game. Therefore, my code that loops through the GamePlays list looking for a non-null Prize must make a call to load each Prize property I check.
I'm not an nhibernate expert, but I know there has to be a better way to do this. Ideally, I'd like to do the following (pseudocode):
entry = findEntry(phoneNumber)
lastPlay = getLatestGamePlay(Entry)
firstWinningPlay = getFirstWinningGamePlay(Entry)
The end result of course is that I have the entry details, the latest game play, and the first winning game play. The catch is that I want to do this in as few database calls as possible, otherwise I'd just execute 3 separate queries.
The object definitions look like:
public class Entry
{
public Guid Id {get;set;}
public string Phone {get;set;}
public IList<GamePlay> GamePlays {get;set;}
// ... other properties
}
public class GamePlay
{
public Guid Id {get;set;}
public Entry Entry {get;set;}
public Prize Prize {get;set;}
// ... other properties
}
public class Prize
{
public Guid Id {get;set;}
// ... other properties
}
The proper NHibernate mappings are in place, so I just need help figuring out how to set up the criteria query (not looking for HQL, don't use it).
since you are doing this in each request maybe it should be better to set up two formula-properties in your entity.
The first one should fetch the latest Gameplay-Id and the other the first Gameplay-Id with a not Null property
this could be as such in the xml mapping file of Entry
<property name="LatestGameplay" formula="select top(1)gp.Id from Gameplay gp where gp.FK_EntryId = PK_EntryId order by gp.InsertDate desc" />
this leaves you with the Gameplay Id's on the Entry entity and after you fetch it it would require another round trip to the DB to GetById-fetch the gameplay's
Alternatively you could work-around using filters.
Set the collection back to "lazy"
and create these nice filters
Gameplay latest = NHibernateSession.CreateFilter(entry.GamePlays , "order by InsertDate desc").SetMaxResults(1).SetFirstResult(1).UniqueResult<Gameplay>();
Gameplay winner = NHibernateSession.CreateFilter(entry.GamePlays , "where FK_PrizeId is not null order by InsertDate asc ").SetMaxResults(1).SetFirstResult(1).UniqueResult<Gameplay>();
And IFilters can be used in a multiquery as so have 2 db hits: one for the original Entry and one for the multiquery.
Last but not least, you could define 2 bags in the Entry entity, one IList<GamePlay> Latest and one IList<Gameplay> Winner which in the Entry mapping file would be filtered with the appropriate query (although i don't remember now if you can define TOP clauses in the filters) and set those as non-lazy. Then with a single round-trip you can have all the data you want with the following (ugly) syntax
Entry entry = findEntry(phoneNumber);
Gameplay winner = entry.Winner[0]; //check this if null first
Gameplay Latest = entry.Latest[0]; //ditto
note that of all the solutions the 3rd is the one that provides a mechanism to generate additional queries, as the bag can be used in a Criteria/HQL query