I have to support linq code that looks like the one below
public async Task<IEnumerable<UserProfiles>> GetUserProfileByIdAsync(IEnumerable<string> ids)
{
.AsQueryable()
.Where(sea => ids.Contains(sea.UserId))
.Distinct()
.ToListAsync()
}
I am only used to writing my linq like this
var query =
from car in cars
join manufacturer in manufacturers ....
what is the difference between the two queries and any link to tutorials
where one can learn how to write the first query with the dots will be
apreciated.
Related
I am creating a Laravel Application with Eloquent connected to MySQL DBMS where I have three models:
Product
ProductGallery
File
I have also the following relations
One Product has one ProductGallery
One ProductGallery has many File
My question is:
Is it okay if I store images in ProductGallery as an array of file_ids
instead of creating a join table or having gallery_id in File model?
public function setImagesAttribute($images)
{
$this->attributes['images'] = serialize($images);
}
public function getImagesAttribute()
{
if (empty($this->attributes['images']) || is_null($this->attributes['images'])) return [];
return unserialize($this->attributes['images']);
}
I am asking this question to know if there is any side effects for this method
and in the future there might be other models related to File model (Category may have featured image file and so on).
In my opinion Better Option is creating a pivot table.. Because further when you have to join , you pull the array and you have to execute a query under a loop that is bad..
How to select a single row on october cms?
How can a simple thing be so complicated here?
I thought it would be something to help us and not to disturb something that is as simple as
SELECT * FROM `engegraph_forms_membros`
Here it's like fighting against demons without a bible, oh god why?
Why make the query difficult for newbie?
I understand you don't speak English natively but you should watch every single one of these videos.
Does the record belong to a model in a plugin? Here are the docs on how to work with models.
You make a plugin, set the database which creates models, and then make components to be ran in your CMS Pages.
In a component.php file you can have something like this: Here I am calling the model class Agreements with use Author\Plugin\Models\Agreements;. This allows me to run a function/method to retrieve all agreements or one agreements using laravel's eloquent collection services.
Lets say we have the ID of a record. Well we can either call on the Agreements model with ::find or with ::where. You will noticed I have two functions that essentially do the same thing. ::find uses the primary key of the models (in my case the id) and will return a singular record. *Note that find can take an array and return a collection of records; like ::where. Using ::where we are going to look for the ID. *Note ::where always returns a collection which is why I have included ->first().
<?php namespace Author\Plugin\Components;
use Session;
use Input;
use Crypt;
use Db;
use Redirect;
use Illuminate\Contracts\Encryption\DecryptException;
use October\Rain\Support\Collection;
use Author\Plugin\Models\Agreements;
class GetAgreement extends \Cms\Classes\ComponentBase
{
public function componentDetails()
{
return [
'name' => 'Get one agreement',
'description' => 'Get an agreement to change or delete it'
];
}
public function onRun() {
$this->page['agreement'] = $this->getWithFindAgreement;
}
public function getWithFindAgreement() {
$id = 1;
$agreement = Agreements::find($id);
return $agreement;
}
public function getWithWhereAgreement() {
$id = 1;
$agreement = Agreements::where($id)->first();
return $agreement;
}
}
If for some reason you aren't working with models, here are the docs to work with Databases. You will have to register the use Db; facade.
Here call the table you want and use ::where to query it. *Note the use of ->first() again.
$users = Db::table('users')->get();
$user = $users->where('id', 1)->first();
There are two simple ways to select a single row:
This will give you the'first' record in the selected recordset.
SELECT top 1 * FROM `engegraph_forms_membros`
This will select all the records that meet the predicate requirement that the value of <columnname> is equal to <value>
SELECT * FROM `engegraph_forms_membros` where <columnname>=<value>
If you select a record where multiple values meet that requirement, then you can (randomly) pick one by combining the solutions...
SELECT top 1 * FROM `engegraph_forms_membros` where <columnname>=<value>
But be aware that without an ORDER BY clause, the underlying data is unordered and prone to change uncontrollably, which is why most people (including your boss) will find the use of 'Top' to be improper for real use.
I have two models (Organizations and Interactions) and I'd like to query the Organization model for all of the Orgs that have no Interactions. Organizations have a one-to-many relationship with Interactions.
I tried looking into anti-joins in raw SQL, but got nowhere. I also wanted to totally avoid anything like getting all of the full Organizations, then iterating through them to check to see if they had any Interactions, because that's completely impractical given the amount of data I'm working with.
To clarify, I want to avoid this:
$organizations = Organization::all();
foreach ($organizations as $org)
if($org->interactions()->count() == 0){
//Add the org to an array for later use because it has no interactions
}
I'm using Laravel 3.x, and I can't upgrade because the project is really big and I don't have the month it would take to upgrade to 4.1 right now. If there's a significantly better way to do stuff like this 4, that would make selling the conversion process easier.
Here's some relevant code:
//From organization.php
public function interactions() {
return $this->has_many('Interaction');
}
//From interaction.php
public function organization() {
return $this->belongs_to('Organization');
}
// select all Organization IDs that have at least 1 interaction
$uniqueOrganizationIDs = DB::raw('SELECT organization_id FROM interactions GROUP BY(organization_id)');
// Select orgs that were not in the above list.
Organization::whereNotIn('id', $uniqueOrganizationIDs)->get();
This is the solution I came up with:
Query the Organization and Interaction models using list(). For Orgs, get their ID. For Interactions, get their organization_id. I figure these are two low-footprint, fast queries.
Do an array_diff() on them to get an array of Organizations that don't have Interactions.
Query Organization using where_in(), feeding it the diff'ed array.
It looks like this:
$organizationIDs = DB::table('organizations')->where('is_deleted', '=', 0)->lists('id');
$interactionIDs = DB::table('interactions')where('is_deleted', '=', 0)->lists('organization_id');
$uncontactedOrganizationIDs = array_diff($organizationIDs, $interactionIDs);
$uncontactedOrganizations = Organization::where_in('id', $uncontactedOrganizationIDs)->order_by('created_at', 'DESC')->get();
Is there a better way to do this? I feel like there has to be.
I am working on a database access layer project and decided to use Linq to SQL for it. One of the things I wanted to do was provide an API that can take Linq Expressions as arguments to retrieve data. For instance, I wrote this API now that looks like this:
public Result GetResults(System.Linq.Expressions.Expression<Func<Result, bool>> predicate)
{
Result result = db.Results.SingleOrDefault(predicate);
return result;
}
You can then use this API to query the database for a Result row that satisfies certain conditions, for example:
Result result = Provider.GetResults(r => r.ID == 11);
This works very well. I am able to get the one row I want based on my conditions.
Next step was taking this to be able to get multiple objects back from the database.
The way I got it to work was like this:
public List<Result> GetResults(System.Linq.Expressions.Expression<Func<Result, bool>> predicate)
{
List<Result> results = db.Results.Select(r => r).Where(r => r.ID == 11).ToList<Result>();
return results;
}
As you can see, I call a Select with r => r, this gives me back everything and then I use a Where to filter to what I need.
It works... but something tells me that I am doing it really ugly. I could be wrong, but doesn't this pull EVERYTHING out of the Results table then filters it? or does it put together the correct SQL statement that does filter at the database level?
Anyway... I would highly appreciate some guidance on how I can accomplish this task. How do I write an API that takes a Linq Expression as an argument and returns a set of objects from the database based on that expression.
Thanks!
The Select(r=>r) does nothing (except change from Table<T> to IQueryable<T> - but nothing useful). And I assume you intended to pass predicate to the Where?
Indeed, this doesn't pull everything out and filter it - the appropriate WHERE (TSQL) clause is generated. This is possible because of "deferred execution" and "composability" - meaning: it doesn't actually execute anything until you start iterating the data (in the ToList()) - until then you are simply shaping the query.
You can see this by doing somthing like:
db.Log = Console.Out;
and look at the TSQL. Or run a TSQL trace. To make it prettier, simplify it to:
return db.Results.Where(predicate).ToList();
I know you said you wanted to pass a predicate and return a List but have you considered returning an IQueryable
Then you could call:
GetResults().Where(r => r.SomeProperty == "SomeValue")
.OrderBy(r => r.SomeOtherProperty)
.Skip(10)
.Take(10); //etc.
With your current API design you would return all records and then have to get 10, where as the above would return only the 10 you needed...
Just some thoughts...
Now that LINQ to SQL is a little more mature, I'd like to know of any techniques people are using to create an n-tiered solution using the technology, because it does not seem that obvious to me.
LINQ to SQL doesn't really have a n-tier story that I've seen, since the objects that it creates are created in the class with the rest of it, you don't really have an assembly that you can nicely reference through something like Web Services, etc.
The only way I'd really consider it is using the datacontext to fetch data, then fill an intermediary data model, passing that through, and referencing it on both sides, and using that in your client side - then passing them back and pushing the data back into a new Datacontext or intellgently updating rows after you refetch them.
That's if I'm understanding what you're trying to get at :\
I asked ScottGu the same question on his blog when I first started looking at it - but I haven't seen a single scenario or app in the wild that uses LINQ to SQL in this way. Websites like Rob Connery's Storefront are closer to the provider.
Hm, Rockford Lhotka sad, that LINQ to SQL is wonderful technology for fetching data from database. He suggests that afterwards they'll must to be bind to "reach domain objects" (aka. CSLA objetcs).
Seriously speaking, LINQ to SQL had it's support for n-tier architecture see DataContext.Update method.
You might want to look into the ADO .Net Entity Framework as an alternative to LINQ to SQL, although it does support LINQ as well. I believe LINQ to SQL is designed to be fairly lightweight and simple, whereas the Entity Framework is more heavy duty and probably more suitable in large Enterprise applications.
OK, I am going to give myself one possible solution.
Inserts/Updates were never an issue; you can wrap the business logic in a Save/Update method; e.g.
public class EmployeesDAL
{
...
SaveEmployee(Employee employee)
{
//data formatting
employee.FirstName = employee.FirstName.Trim();
employee.LastName = employee.LastName.Trim();
//business rules
if(employee.FirstName.Length > 0 && employee.LastName.Length > 0)
{
MyCompanyContext context = new MyCompanyContext();
//insert
if(employee.empid == 0)
context.Employees.InsertOnSubmit(employee);
else
{
//update goes here
}
context.SubmitChanges();
}
else
throw new BusinessRuleException("Employees must have first and last names");
}
}
For fetching data, or at least the fetching of data that is coming from more than one table you can use stored procedures or views because the results will not be anonymous so you can return them from an outside method. For instance, using a stored proc:
public ISingleResult<GetEmployeesAndManagersResult> LoadEmployeesAndManagers()
{
MyCompanyContext context = new MyCompanyContext();
var emps = context.GetEmployeesAndManagers();
return emps;
}
Seriously speaking, LINQ to SQL had it's support for n-tier architecture see DataContext.Update method
Some of what I've read suggests that the business logic wraps the DataContext - in other words you wrap the update in the way that you suggest.
The way i traditionally write business objects i usually encapsulate the "Load methods" in the BO as well; so I might have a method named LoadEmployeesAndManagers that returns a list of employees and their immediate managers (this is a contrived example) . Maybe its just me, but in my front end I'd rather see e.LoadEmployeesAndManagers() than some long LINQ statement.
Anyway, using LINQ it would probably look something like this (not checked for syntax correctness):
var emps = from e in Employees
join m in Employees
on e.ManagerEmpID equals m.EmpID
select new
{ e,
m.FullName
};
Now if I understand things correctly, if I put this in say a class library and call it from my front end, the only way I can return this is as an IEnumerable, so I lose my strong typed goodness. The only way I'd be able to return a strongly typed object would be to create my own Employees class (plus a string field for manager name) and fill it from the results of my LINQ to SQL statement and then return that. But this seems counter intuitive... what exactly did LINQ to SQL buy me if I have to do all that?
I think that I might be looking at things the wrong way; any enlightenment would be appreciated.
"the only way I can return this is as an IEnumerable, so I lose my strong typed goodness"
that is incorrect. In fact your query is strongly typed, it is just an anonymous type. I think the query you want is more like:
var emps = from e in Employees
join m in Employees
on e.ManagerEmpID equals m.EmpID
select new Employee
{ e,
m.FullName
};
Which will return IEnumerable.
Here is an article I wrote on the topic.
Linq-to-sql is an ORM. It does not affect the way that you design an N-tiered application. You use it the same way you would use any other ORM.
#liammclennan
Which will return IEnumerable. ... Linq-to-sql is an ORM. It does not affect the way that you design an N-tiered application. You use it the same way you would use any other ORM.
Then I guess I am still confused. Yes, Linq-to-Sql is an ORM; but as far as I can tell I am still littering my front end code with inline sql type statements (linq, not sql.... but still I feel that this should be abstracted away from the front end).
Suppose I wrap the LINQ statement we've been using as an example in a method. As far as I can tell, the only way I can return it is this way:
public class EmployeesDAL
{
public IEnumerable LoadEmployeesAndManagers()
{
MyCompanyContext context = new MyCompanyContext();
var emps = from e in context.Employees
join m in context.Employees
on e.ManagerEmpID equals m.EmpID
select new
{ e,
m.FullName
};
return emps;
}
}
From my front end code I would do something like this:
EmployeesDAL dal = new EmployeesDAL;
var emps = dal.LoadEmployeesAndManagers();
This of course returns an IEnumerable; but I cannot use this like any other ORM like you say (unless of course I misunderstand), because I cannot do this (again, this is a contrived example):
txtEmployeeName.Text = emps[0].FullName
This is what I meant by "I lose strong typed goodness." I think that I am starting to agree with Crucible; that LINQ-to-SQL was not designed to be used in this way. Again, if I am not seeing things correctly, someone show me the way :)