i have in my database a User has list of Subscriptions, each subscription has a Category, each category has list of Paths, each path has list of Articles ?
Model
class User {
ICollection<Subscription> Subscriptions;
}
class Subscription {
Category category;
}
class Category {
ICollection<Path> paths;
}
class Path{
ICollection<Article> Articles;
}
my question
How to retrieve all Articles for a specific user ?
Using a combination of Select and SelectMany statements, you are able to traverse your entities and find the collection you need:
var allUserArticles = myUser.Subscriptions
.Select(sub => sub.Category) //take the category from each subscription
.SelectMany(cat => cat.Paths) //Take each path from each category, put them in a single list
.SelectMany(path => path.Articles) //Take each article from each path, put them in a single list
.ToList();
Note that if these entities need to be loaded from your database, that EF either needs to implement eager loading, or you have to make sure that all needed related entities are retrieved before running the above statement. Unexpected nulls can cause your output to be incorrect.
However, I have no info on this as it is missing from the question, so I can't know your specific case.
Related
/Countries/Lebanon/Governorates/Mount Lebanon/Districts/Chouf/Cities/Wadi al-Zayneh/Data/Products/Main Categories/Restaurants & Bakeries/Sub Categories/Snack/Sub Categories/Abo Arab Cafe
So as you can see, this is a snippet from my current Firestore structure. So many deeply nested collections. The issue is, I want to keep going deeper as long as a collection called 'Sub Categories' is found which in that case I would render them in the UI. And when eventually I reach a level where 'Sub Categories' is not found, I will render a different UI and show the actual products (The last document "Abo Arab Cafe" contains all the products as maps). The pattern of how many Sub Categories there are is unexpectable and can be modified by the end user.
How can I keep checking for Sub Categories? How to manage my queries in a way that they are dynamically generated at each level at the client-side?
I use Flutter. Here is my current queries structure:
import 'package:cloud_firestore/cloud_firestore.dart';
class FirebaseServices {
final FirebaseFirestore _db = FirebaseFirestore.instance;
CollectionReference mainCategoryCollectionReference() {
CollectionReference mainCategoryCollectionReference = _db.collection(
'/Countries/Lebanon/Governorates/Mount Lebanon/Districts/Chouf/Cities/Wadi al-Zayneh/Data/Products/Main Categories');
return mainCategoryCollectionReference;
}
CollectionReference subCategoryCollectionReference(
String parentSelectedCategory) {
CollectionReference mainCategoryCollectionReference = _db.collection(
'/Countries/Lebanon/Governorates/Mount Lebanon/Districts/Chouf/Cities/Wadi al-Zayneh/Data/Products/Main Categories/$parentSelectedCategory/Sub Categories');
return mainCategoryCollectionReference;
}
bool checkIfSubCategoriesExist(CollectionReference collectionReference) {
bool subCategoriesExist;
collectionReference.get().then((value) => {
subCategoriesExist = value.docs.isNotEmpty,
print('SubCategoriesExist: $subCategoriesExist')
});
return subCategoriesExist;
}
}
This works only if I know for certain how many levels of deepness there are, but since this can be modified by the user, it won't work.
Sorry for the very long question I had no idea how to explain it properly and clearly. Thank you in advance!
The structure is all wrong, there is no point in the structure being this deeply nested. The structure of the database needs to match what has to appear in the UI.
Assuming this is a worldwide application since you are using countries then you have to do the following:
Collection
Document
Fields
Countries
Random ID
countryName - arrayOfDistrict- arrayOfGovernorates
3 Fields under each document id, containing information about the country.
Then regarding Resturants:
Collection
Document
Fields
SubCollection
subCollectionId
Fields
Resturant
Random ID
resturant_name- resturant_location - info_about_resturant
Menu
randomId
dish_name - price -...
The problem with your db structure is that it is very nested instead of making a flat structure and that right now you are harcoding the whole path.
Using the above structure, you can create a dropdown with list of countries if the user chooses Lebanon, then you get the districts and the governorates. Then you can do a call to get the resturants that are inside each district, since in the documents inside Resturant collection you can get location of each resturant and name.
After that on click of each resturant, you will get the data inside the subcollection that will contain the full menu.
I think I found the solution with the help of a friend!
Since the checkIfSubCategoriesExist function is always checking on the very last reached level(using the collectionReference argument) whether Sub Categories exists or not, he suggested that in case it does exist, I can append to its argument collectionReference the new "Sub Categories" String to the path as a variable! This way I can query on it and voila!
I am using Entity Framework 7 Code First
I have a function that needs to returns a list of Countries(ids,Names) linked to a User.
The User isn't directly linked to the Country but is linked via the City. City is linked to State. State is linked to Country.
I decided to use a GroupBy to get the list of countries.
public async Task<IEnumerable<Country>> Search(int userId)
{
var table = await _db.Cities
.Include(ci => ci.States.Country)
.Select(ci => ci.States.Country)
.OrderBy(co => co.CountryName)
.GroupBy(co=>co.pk_CountryId)
.ToListAsync()
;
return table;
}
However I get the error:
CS0266 Cannot implicitly convert type
'System.Collections.Generic.List <System.Linq.IGrouping> to
'System.Collections.Generic.List'
How do I return a variable IEnumerable<Country> as that is what the receiving code expects i.e. a list of Countries?
Am I doing my grouping correct?
For performance I assume grouping is better than a distinct or a contains
If you want to have the distinct countries, you can use a select afterwards to select the first country in each IGrouping<int,Country>:
public async Task<IEnumerable<Country>> Search(int userId)
{
return await _db.Cities
.Include(ci => ci.States.Country)
.Select(ci => ci.States.Country)
.OrderBy(co => co.CountryName)
.GroupBy(co=>co.pk_CountryId)
.Select(co => co.FirstOrDefault())
.ToListAsync();
}
Also a little sidenote, the Include isn't necessary here, eager loading the countries would only be useful if you were to return the States and wanted its Country property be populated. The Select makes sure you're grabbing the Country, you're not even fetching the states anymore from database.
Just starting out with Entity Framework and am trying to work out how you would do something like this....
Say I have the following entities, Customers that have Orders that have OrderLineItems which are linked to Products. I would like to return the name of every customer with a count of the number of times they have ordered a particular product.
I have seen examples of using .Count() but these have always been for the first navigation property i.e. number of orders per customer.
Would appreciate some guidance here.
Something like this should work, where context is your DbContext instance.
It will return an IEnumerable<dynamic>, although obviously you could make a class to hold the results.
// The product to count
var productId = 12345;
context.Customers.Include("Orders.OrderLineItems.Products")
.Select(customer =>
new {
CustomerName = customer.Name,
ProductCount = customer.Orders
.SelectMany(o => o.OrderLineItems)
.SelectMany(i => i.Products.Where(p => p.Id = productId).Count()
});
The Include() extension method is useful, it will make sure that the resulting SQL query joins the relevant tables together - otherwise multiple queries would be executed for each customer (one to get orders, another for line items and a final one for products).
I need to query a collection based on a list of parameters.
For example my model is:
public class Product
{
string id{get;set;}
string title{get;set;}
List<string> tags{get;set;}
DateTime createDate{get;set;}
DbReference<User> owner{get;set;}
}
public class User
{
string id{get;set;}
...other properties...
}
I need to query for all products owned by specified users and sorted by creationDate.
For example:
GetProducts(List<string> ownerIDs)
{
//query
}
I need to do it in one query if possible not inside foreach. I can change my model if needed
It sounds like you are looking for the $in identifier. You could query products like so:
db.product.find({owner.$id: {$in: [ownerId1, ownerId2, ownerId3] }}).sort({createDate:1});
Just replace that javascript array [ownerId1, ...] with your own array of owners.
As a note: I would guess this query is not very efficient. I haven't had much luck with DBRefs in MongoDB, which essentially adds relations to a non-relational database. I would suggest simply storing the ownerID directly in the product object and querying based on that.
The solution using LINQ is making an array of user IDs and then do .Contains on them like that:
List<string> users = new List<string>();
foreach (User item in ProductUsers)
users .Add(item.id);
return MongoSession.Select<Product>(p => users .Contains(p.owner.id))
.OrderByDescending(p => p.createDate)
.ToList();
First of I am new to ORMLite. I would like my model class to have a field which is a list of strings, that would eventually hold a list of tags for my model object.
Which ORMLite annotations should I use?
Firstly I don't want to have a table of all tags, and then use the #ForeignCollectionField.
Also I thought of using the #DatabaseField(dataType=DataType.SERIALIZABLE) annotation, but it turns out that List<String> doesn't implement the Serializable interface.
What are your suggestions?
First of all, List doesn't implement Serializable but ArrayList certainly does as well as most of the common collection implementations. But storing a huge list is probably not the best of doing this from a pure object model standpoint.
So why don't you want to have a table of all tags? That's the best way from a pure model standpoint. It will require a 2nd query if you need them every time. That's the way hibernate would store a list or array of tags.
After reading your comment #creen, I still think you do want a table of tags. Your model class would then have:
#ForeignCollectionField
Collection<Tag> tags;
The tags table would not have a single tag named "red" with multiple model classes referring to it but multiple "red" entries. It would look like:
model_id name
1 "red"
1 "blue"
2 "red"
3 "blue"
3 "black"
Whenever you are removing the model object, you would first do a tags.clear(); which would remove all of the tags associated with that model from the tags table. You would not have to do any extra cleanup or anything.
No need to go for #ForeignCollectionField for simple String Array
Change your code
#DatabaseField(dataType=DataType.SERIALIZABLE)
List<String> users;
to
#DatabaseField(dataType = DataType.SERIALIZABLE)
String[] users;
Database doesn't want to store dynamically grow able arrays. That is the reason it allows only static array like string[] and not List.
I added two properties... one that gets written to the database as a csv string and the other that translates this:
[Ignore]
public List<string> Roles
{
get
{
return new List<string>(RolesCsv.Split(new char[] { ',' }));
}
set
{
RolesCsv = string.Join(",", value);
}
}
public string RolesCsv { get; set; }