How do I retrieve a hierarchical tree structure with a linq query and EF?
My database has tables for Tab which is 1-to-Many to TabGroupBox which is 1-to-Many to FieldDetail
I would like to retrieve only portions of the structure based on some criteria.
Say, I have the following in the database:
Tab (Name)
"Tab1"
"Tab2"
"Tab3"
TabGroupBox (Tab.Name, Name)
"Tab1", "Group1"
"Tab2", "Group2"
"Tab1", "Group3"
FieldDetail: (TabGroupBox.Name, Name, FieldStatus)
"Group1", "Field1", "Good1"
"Group2", "Field2", "Good2"
"Group3", "Field3", "Bad"
"Group1", "Field4", "Good3"
"Group1", "Field5", "Bad"
If the criteria is for the FieldStatus to contain "Good", then the result I'm looking for is:
Tab1
-Group1
--Field1
--Field4
Tab2
-Group2
--Field2
However, at the moment can only seem to get either
Field1
Field2
Field4
or a duplication of tabs corresponding to the fields
Tab1
Tab1
Tab2
A sample of my non-working query:
Tabs.SelectMany(x => x.TabGroupBoxes.SelectMany(y => y.FieldDetails).Where(z =>
(z.FieldDetailType.Contains("Good")
))
.Select(x => x.TabGroupBox.Tab)
I've also tried making use of .Include() but no success
Additionally, if possible, I'd like to project the db models onto my view models within the query, but this is not as important as above.
The best you can do is the following.
context.FieldDetails
.Include(fieldDetail => fieldDetail.GroupBox.Tab) // Use eager loading.
.Where(fieldDetail => fieldDetail.FieldDetailType.Contains("Good")))
.AsEnumerable() // We will do the remaining work client side.
.Select(fieldDetail => fieldDetail.GroupBox.Tab)
.Distinct() // Get rid of duplicate tabs.
.ToList()
What is not easily possible is to retrieve a collection of related entites partially, for example only Group1 but not Group3 for Tab1. If you could do this it would cause some headaches. What if you commit changes for Tab1? Should Group3 get deleted because it is not present in the collection of groups? Should it stay because you did not load it in the first place? If you think about it for some time you will realize that the ability to partially load collections of related entities would add a lot of complexity and make the behavior very non-intuitive in some cases.
If this is not enough you might be able to create views or functions in the database and map these to your model but I have not used the Entity Framework for more than two years and did not follow the development so I can not provide you more details how to approach this.
Related
I am trying to build a custom sorting for the product listings in shopware 6.
I want to include a foreign table (entity is: leasingPlanEntity), get the min of one of the fields of that table (period_price) and then order the search result by that value.
I have already built a Subscriber, and try it like that, what seems to work.
public static function getSubscribedEvents(): array
{
return [
//ProductListingCollectFilterEvent::class => 'addFilter'
ProductListingCriteriaEvent::class => ['addCriteria', 5000]
];
}
public function addCriteria(ProductListingCriteriaEvent $event): void
{
$criteria = $event->getCriteria();
$criteria->addAssociation('leasingPlan');
$criteria->addAggregation(new MinAggregation('min_period_price', 'leasingPlan.periodPrice'));
// Sortierung hinzufügen.
$availableSortings = $event->getCriteria()->getExtension('sortings') ?? new ProductSortingCollection();
$myCustomSorting = new ProductSortingEntity();
$myCustomSorting->setId(Uuid::randomHex());
$myCustomSorting->setActive(true);
$myCustomSorting->setTranslated(['label' => 'My Custom Sorting at runtime']);
$myCustomSorting->setKey('my-custom-runtime-sort');
$myCustomSorting->setPriority(5);
$myCustomSorting->setFields([
[
'field' => 'leasingPlan.periodPrice',
'order' => 'asc',
'priority' => 1,
'naturalSorting' => 0,
],
]);
$availableSortings->add($myCustomSorting);
$event->getCriteria()->addExtension('sortings', $availableSortings);
}
Is this already the right way to get the min(periodPrice)? Or is it taking just a random value out of the leasingPlan table to define the sort-order?
I didn't find a way, to define the min_period_price aggregate value in the $myCustomSorting->setFields Methods.
Update 1
Some days later, I asked a less complex question in the shopware community on slack:
Is it possible to use the DAL to define a subquery for an association in the product-listing?
It should generate something like:
FROM
JOIN (
SELECT ... FROM ... WHERE ... GROUP BY ... ORDER BY ...
) AS ...
The answer there was:
Don't think so
Update 2
I also did an in-deep anlysis of the DAL-Query-Builder, and it really seems to be not possible, to perform a subquery with the current version.
Update 3 - Different approach
A different approach might be, to define custom fields in the main entity. Every time a change is made on the main entity, the values of this custom fields should be recalculated.
It is a lot of overhead work, to realize this. Especially when the fields you are adding, are dependend on other data like the availability of a product in the store, for example.
So check, if it is worth the extra work. Would be better, to have a solution for building subqueries.
Unfortunately it seems that in your case there is no easy way to achieve this, if I understand the issue correctly.
Consider the following: for each product you can have multiple leasingPlan entities, and I assume that for a given context (like a specific sales channel or listing) that still holds. This means that you would have to sort the leasingPlan entities by price, then take the one with the lowest price, and then sort the products by their lowest-price leasingPlan's price.
There seems to be no other way to achieve that, and unfortunately for you, sorting is applied at the end, even if it is sort of a subquery.
So, for example, if you have the following snippet
$criteria = $event->getCriteria();
$criteria->addAssociation('leasingPlan');
$criteria->getAssociation('leasingPlan')
->addSorting(new FieldSorting('price', FieldSorting::ASCENDING))
->setLimit(1)
;
The actual price-sorting would be applied AFTER the leasingPlan entities are fetched - essentially the results would be sorted, meaning that you would not get the cheapest leasing plan per product, instead getting the first one.
You can only do something like that with filters, but in this case there is nothing to filter by - I assume you don't have one leasingPlan per SalesChannel or per language, so that you could limit that list to just one entry that could be used for sorting
That is not to mention that this could not be included in a ProductSortingEntity, but you could always work around that by plugging into the appropriate events and modifying the criteria during runtime
I see two ways to resolve your issue
Making another table which would store the cheapest leasingPlan per product and just using that as your association
Storing the information about the cheapest leasingPlans in e.g. cache and using that for filtering (caution: a mistake here would probably break the sorting, for example if you end up with too few or too many leasingPlans per product)
public function applyCustomSorting(ProductListingCriteriaEvent $event): void
{
// One leasingPlan per one product
$cheapestLeasingPlans = $this->myCustomService->getCheapestLeasingPlanIds();
$criteria = $event->getCriteria();
$criteria->addAssociation('leasingPlan');
$criteria->getAssociation('leasingPlan')
->addSorting(new FieldSorting('price', FieldSorting::ASCENDING))
->addFilter(new EqualsAnyFilter('id', $cheapestLeasingPlans))
;
}
And then you could sort by
$criteria->addSorting(new FieldSorting('leasingPlan.periodPrice', FieldSorting::ASCENDING));
There should be no need to add the association manually and to add the aggregation to the criteria, that should happen automatically behind the scenes if your custom sorting is selected in the storefront.
For more information refer to the official docs.
Say I have a user table with a property called favoriteUsers which is an embedded array. i.e.
users
{
name:'bob'
favoriteUsers:['jim', 'tim'] //can you have an index on an embedded array?
}
user_presence
{
name:'jim', //index on name
online_since:14440000
}
Can I do an inner or eqJoin against say a 2nd table using the embedded property, or would I have to pull favoriteUsers out of the users table and into a join table like in traditional sql?
r.table('users')
.getAll('bob', {index:'name'})
// inner join user_presence on user_presence.name in users.highlights
.eqJoin("name", r.table('user_presence'), {index:'name'})
Eventually, I'd like to call changes() on the query so that I can get a realtime update of the users favorite users presence changes
eqJoin can works on embedded document, but it works by compare a value which we transform/pick from the embedded document to mark secondary index on right table.
In any other complicated join, I would rather use concatMap together with getAll.
Let's say we can fetch user and user_presence of their favoriteUsers
r.table('users')
.getAll('bob', {index: 'name'})
.concatMap(function(user) {
return r.table('user_presence').filter(function(presence) {
return user("favoriteUsers").contains(presence("name"))
})
)
So ideally, now you get the data and do the join yourself by querying extra data that you need. My query may have some syntax/error but I hope it gives you the idea
I am a new user of RethinkDB. Could anyone tell me if every time that I receive changes on a table, through the Changefeeds feature, the query needs to reevaluated every time?
For example, a query that return all the users from a specified country. Two tables: users and countries. I allways want to know all the users from that country. I ask because if my table has a lot of records (millions) could be a bit expensive...
Thanks in advance,
Humberto
The answer is... it depends on what you want to do and how your query is structured.
#1 Simple Queries
If you have a simple filter query that is listening for changes on all 'users' from a particular country, your query won't get reevaluated every single time. RethinkDB handles that automatically and it's not an expensive operation. In terms of performance, this is the preferred strategy.
Example:
r.table('users')
.filter({ country: "China })
.changes()
You can also listen to users from multiple countries in the same query:
var countries = [ 'China', 'India', 'Colombia', 'Mexico', 'United States' ];
r.table('users')
.filter(function (row) {
return r.expr(countries).contains(row('country'));
})
.changes()
#2 Simple Queries with single join
If, when you get an update on the user, but you also want to join the country data from the 'countries' table, you can do that after the changes with a merge and a get.
r.table('users')
.filter({ country_name: "China })
.changes()
.merge(function (row) {
return {
'country': r.table('countries').get(row('country_name'))
}
})
This will join the data every time there's an update, but it's more expensive than the previous one because, every time there is an update, it will have to do a point read in the 'countries' table.
#3 Alternative to #2
If you don't want to do this, but want to still join the countries to the 'users' table, you could do the joins in your application layer.
I need some help constructing a LINQ expression. I tend to use Lambda syntax.
I have 2 tables
OrderItem >- LibraryItem
OrderItem has a number of columns:
Id
FkLibraryItemId
Text
FkOrderId
LibraryItem has a number of Columns:
Id
Text
Type
Usually when selecting an "OrderItem", one picks a "Library Item". The "Id" and "Text" value are placed into the item record.
Sometimes a user may add a one off "OrderItem" which does not need storing in the "LibraryItem" table. It is simply stored in "OrderItem", but without a "FkLibraryItemId". So I have records in "OrderItem" that do not exist in "LibraryItem".
I need the LINQ to pull out all the relevant "LibraryItem" records of "Type=X" in addition to the "OrderItem" records for the relevant Order Id.
Many thanks in advance.
UPDATE:
I think I am talking about something like:
LibraryItem.Select(new{Id,Text}).Union(Order.Select(new{Id, Text})
context.OrderItems.Include("LibraryItems")
.Where(o => o.OrderId == orderId
&&(o.LibraryItem != null ? o.LibraryItem.Type == "X" : true))
Linq-to-SQL has a different syntax for Include, which basically eager-loads the reference objects (probably LoadWith, I don't remember at the moment).
Actually you can also do it with left inner join.
Let's say I have an Order table which has a FirstSalesPersonId field and a SecondSalesPersonId field. Both of these are foreign keys that reference the SalesPerson table. For any given order, either one or two salespersons may be credited with the order. In other words, FirstSalesPersonId can never be NULL, but SecondSalesPersonId can be NULL.
When I drop my Order and SalesPerson tables onto the "Linq to SQL Classes" design surface, the class builder spots the two FK relationships from the Order table to the SalesPerson table, and so the generated Order class has a SalesPerson field and a SalesPerson1 field (which I can rename to SalesPerson1 and SalesPerson2 to avoid confusion).
Because I always want to have the salesperson data available whenever I process an order, I am using DataLoadOptions.LoadWith to specify that the two salesperson fields are populated when the order instance is populated, as follows:
dataLoadOptions.LoadWith<Order>(o => o.SalesPerson1);
dataLoadOptions.LoadWith<Order>(o => o.SalesPerson2);
The problem I'm having is that Linq to SQL is using something like the following SQL to load an order:
SELECT ...
FROM Order O
INNER JOIN SalesPerson SP1 ON SP1.salesPersonId = O.firstSalesPersonId
INNER JOIN SalesPerson SP2 ON SP2.salesPersonId = O.secondSalesPersonId
This would make sense if there were always two salesperson records, but because there is sometimes no second salesperson (secondSalesPersonId is NULL), the INNER JOIN causes the query to return no records in that case.
What I effectively want here is to change the second INNER JOIN into a LEFT OUTER JOIN. Is there a way to do that through the UI for the class generator? If not, how else can I achieve this?
(Note that because I'm using the generated classes almost exclusively, I'd rather not have something tacked on the side for this one case if I can avoid it).
Edit: per my comment reply, the SecondSalesPersonId field is nullable (in the DB, and in the generated classes).
The default behaviour actually is a LEFT JOIN, assuming you've set up the model correctly.
Here's a slightly anonymized example that I just tested on one of my own databases:
class Program
{
static void Main(string[] args)
{
using (TestDataContext context = new TestDataContext())
{
DataLoadOptions dlo = new DataLoadOptions();
dlo.LoadWith<Place>(p => p.Address);
context.LoadOptions = dlo;
var places = context.Places.Where(p => p.ID >= 100 && p.ID <= 200);
foreach (var place in places)
{
Console.WriteLine(p.ID, p.AddressID);
}
}
}
}
This is just a simple test that prints out a list of places and their address IDs. Here is the query text that appears in the profiler:
SELECT [t0].[ID], [t0].[Name], [t0].[AddressID], ...
FROM [dbo].[Places] AS [t0]
LEFT OUTER JOIN (
SELECT 1 AS [test], [t1].[AddressID],
[t1].[StreetLine1], [t1].[StreetLine2],
[t1].[City], [t1].[Region], [t1].[Country], [t1].[PostalCode]
FROM [dbo].[Addresses] AS [t1]
) AS [t2] ON [t2].[AddressID] = [t0].[AddressID]
WHERE ([t0].[PlaceID] >= #p0) AND ([t0].[PlaceID] <= #p1)
This isn't exactly a very pretty query (your guess is as good as mine as to what that 1 as [test] is all about), but it's definitively a LEFT JOIN and doesn't exhibit the problem you seem to be having. And this is just using the generated classes, I haven't made any changes.
Note that I also tested this on a dual relationship (i.e. a single Place having two Address references, one nullable, one not), and I get the exact same results. The first (non-nullable) gets turned into an INNER JOIN, and the second gets turned into a LEFT JOIN.
It has to be something in your model, like changing the nullability of the second reference. I know you say it's configured as nullable, but maybe you need to double-check? If it's definitely nullable then I suggest you post your full schema and DBML so somebody can try to reproduce the behaviour that you're seeing.
If you make the secondSalesPersonId field in the database table nullable, LINQ-to-SQL should properly construct the Association object so that the resulting SQL statement will do the LEFT OUTER JOIN.
UPDATE:
Since the field is nullable, your problem may be in explicitly declaring dataLoadOptions.LoadWith<>(). I'm running a similar situation in my current project where I have an Order, but the order goes through multiple stages. Each stage corresponds to a separate table with data related to that stage. I simply retrieve the Order, and the appropriate data follows along, if it exists. I don't use the dataLoadOptions at all, and it does what I need it to do. For example, if the Order has a purchase order record, but no invoice record, Order.PurchaseOrder will contain the purchase order data and Order.Invoice will be null. My query looks something like this:
DC.Orders.Where(a => a.Order_ID == id).SingleOrDefault();
I try not to micromanage LINQ-to-SQL...it does 95% of what I need straight out of the box.
UPDATE 2:
I found this post that discusses the use of DefaultIfEmpty() in order to populated child entities with null if they don't exist. I tried it out with LINQPad on my database and converted that example to lambda syntax (since that's what I use):
ParentTable.GroupJoin
(
ChildTable,
p => p.ParentTable_ID,
c => c.ChildTable_ID,
(p, aggregate) => new { p = p, aggregate = aggregate }
)
.SelectMany (a => a.aggregate.DefaultIfEmpty (),
(a, c) => new
{
ParentTableEntity = a.p,
ChildTableEntity = c
}
)
From what I can figure out from this statement, the GroupJoin expression relates the parent and child tables, while the SelectMany expression aggregates the related child records. The key appears to be the use of the DefaultIfEmpty, which forces the inclusion of the parent entity record even if there are no related child records. (Thanks for compelling me to dig into this further...I think I may have found some useful stuff to help with a pretty huge report I've got on my pipeline...)
UPDATE 3:
If the goal is to keep it simple, then it looks like you're going to have to reference those salesperson fields directly in your Select() expression. The reason you're having to use LoadWith<>() in the first place is because the tables are not being referenced anywhere in your query statement, so the LINQ engine won't automatically pull that information in.
As an example, given this structure:
MailingList ListCompany
=========== ===========
List_ID (PK) ListCompany_ID (PK)
ListCompany_ID (FK) FullName (string)
I want to get the name of the company associated with a particular mailing list:
MailingLists.Where(a => a.List_ID == 2).Select(a => a.ListCompany.FullName)
If that association has NOT been made, meaning that the ListCompany_ID field in the MailingList table for that record is equal to null, this is the resulting SQL generated by the LINQ engine:
SELECT [t1].[FullName]
FROM [MailingLists] AS [t0]
LEFT OUTER JOIN [ListCompanies] AS [t1] ON [t1].[ListCompany_ID] = [t0].[ListCompany_ID]
WHERE [t0].[List_ID] = #p0