Suppose the following mapped classes:
public class Item
{
public virtual int Id { get; set; }
public virtual IEnumerable<History> Histories { get; set; }
}
public class History
{
public virtual int Id { get; set; }
public virtual Item Item { get; set; }
public virtual DateTime Date { get; set; }
public virtual HistoryType HistoryType { get; set; }
}
public enum HistoryType
{
A = 1,
B = 2
}
Now I want to be able to fetch all items ordered by their latest History Date, where History is of HistoryType = A. Not all items have history so I guess a left join is needed.
What I need is a query for Fluent NHibernate but it would also be nice to see a correct SQL query for this.
Standard SQL Query for your case will look like this. Yes you need a Left Join to get all items.
all items ordered by their latest History Date, where History is of HistoryType = A. even for items that has not hisotry
SELECT i.id, h.id, h.datetime, h.historytype
FROM ITEMS i
LEFT JOIN HISTORY h
ON i.id = h.itemid
WHERE h.HistoryType = 'A'
ORDER BY h.Datetime DESC
If you choose to show a user-defined value istead of null. E.g. when an item has no history, history table reocrds returned will be null. Thus a function like Colasce could help you to add syntatic sugar to your query :)
Please apply the correct syntax (e.g. whether to use backtics/inverted commas for String/varchar columns values) for Fluent NHibernate.
Related
I have List of Orders, which have the property "Status" which is an int. For each status I have a translations in different languages. I want to sort my list by the selected translation and not by numeric status value. What is the best practice here?
public record OrderTranslation
{
public string OrderStatus { get; set; }
public string StatusDescription { get; set; }
public Language Language { get; set; }
}
public record Order
{
public int? Id { get; set; }
public int Status { get; set; }
// I have added a new value to set the translated value and I want to order by this
public string TranslatedStatusValue { get; set;}
}
my function:
public async Task<FilterResult> FilterAsync(FilterRequest filterRequest, List<string> filterProperties, Language selectedLanguage)
{
var orderTranslations = dataContext
.OrderTranslations
.Where(ot => ot.Language == selectedLanguage)
.ToList();
var orders = dataContext.Orders.AsNoTracking();
foreach (var order in orders)
{
var description = orderTranslations
.Single(x => x.OrderStatus == serviceContract.Status)
.StatusDescription;
serviceContract.TranslatedValue = description;
}
// The TranslatedValue is always empty here
// This is not working, but I want to Order by the translation. Is there another possibility to to this, not using an extra property?
IQueryable<ServiceContractOrder> query = orders
.OrderBy("TranslatedStatusValue", filterRequest.IsSortAscending)
.WhereMatchesFilter(filterRequest, filterProperties);
result.FilterHits = await query
.Skip(filterRequest.ItemsToSkip())
.Take(filterRequest.ItemsPerPage)
.Cast<object>()
.ToListAsync();
result.TotalCount = await query.CountAsync();
result.ObjectType = typeof(Order).AssemblyQualifiedName;
result.FilteredProperties = filterProperties;
}
It all depends on your size of data and what you want to achieve.
If you have small data set, without pagination, you can sort them in client side ( in your dotnet code).
If you have a large dataset, and/or you need pagination, then you will need to apply the sorting to the DB. In such case, I would suggest you to store the translated values in Same table as Owned Entity or maybe different table. And then you can apply sorting in your LINQ query.
Two benefits you get is,
Sorting is absolute, and order is maintained across queries.
Performance, as sorting on client-side hurts for large data sets.
What you lose,
Any change to translation has to be applied to DB. This makes your database complex.
If the order status is a fixed set of data, like enum, then you can chose to have a denormalized design. i.e., to have a dedicated OrderStatus table with translations and then join them to your Order table.
Your domain will be somewhat like,
public record OrderStatus
{
int Id{get; set;}
public ISet<OrderTranslation> Translations { get; set; }
}
public record OrderTranslation(Language Language, string)
{
public string OrderStatus { get; set; }
public string StatusDescription { get; set; }
public Language Language { get; set; }
}
public record Order
{
public int? Id { get; set; }
public OrderStatus Status { get; set; }
}
As of now, I am trying to create a list that groups based on certain criteria and then display that list in the view.
I have two database tables and one is an association table.
First Table
public partial class InitialTraining
{
public InitialTraining()
{
InitialTrainingAssociations = new HashSet<InitialTrainingAssociation>();
}
public int Id { get; set; }
[ForeignKey("MedicInfo")]
public int TfoId { get; set; }
[ForeignKey("InstructorInfo")]
public int? InstructorId { get; set; }
[ForeignKey("PilotInfo")]
public int? PilotId { get; set; }
public DateTime DateTakenInitial { get; set; }
public decimal FlightTime { get; set; }
public bool Active { get; set; }
[StringLength(2000)]
public string Narrative { get; set; }
[Required]
[StringLength(20)]
public string TrainingType { get; set; }
[ForeignKey("CodePhase")]
public int PhaseId { get; set; }
[ForeignKey("PhaseTrainingType")]
public int PhaseTrainingTypeId { get; set; }
public string EnteredBy { get; set; }
public DateTime? EnteredDate { get; set; }
public virtual MedicInfo MedicInfo { get; set; }
public virtual MedicInfo InstructorInfo { get; set; }
public virtual MedicInfo PilotInfo { get; set; }
public virtual Code_Phase CodePhase { get; set; }
public virtual Code_PhaseTrainingType PhaseTrainingType { get; set; }
public virtual ICollection<InitialTrainingAssociation> InitialTrainingAssociations { get; set; }
}
Second Table (Association Table)
public class InitialTrainingAssociation
{
public int Id { get; set; }
[ForeignKey("InitialTraining")]
public int InitialTrainingId { get; set; }
[ForeignKey("CodePerformanceAnchor")]
public int? PerformanceAnchorId { get; set; }
[ForeignKey("GradingSystem")]
public int? GradingSystemId { get; set; }
public virtual AviationMedicTraining.CodePerformanceAnchor CodePerformanceAnchor { get; set; }
public virtual InitialTraining InitialTraining { get; set; }
public virtual GradingSystem GradingSystem { get; set; }
}
Here is my GroupBy in C#.
// get list of initial training record ids for statistics
var lstInitialTrainings = db.InitialTrainings.Where(x => x.TfoId == medicId && x.Active).Select(x => x.Id).ToList();
// get list of initial training performance anchors associated with initial training records
var lstPerformanceAnchors = db.InitialTrainingAssociations
.Where(x => lstInitialTrainings.Contains(x.InitialTrainingId)).GroupBy(t => t.PerformanceAnchorId)
.Select(s => new MedicStatistic()
{
PerformanceAnchorName = db.CodePerformanceAnchor.FirstOrDefault(v => v.Id == s.Key).PerformanceAnchor,
AnchorCount = s.Count()
}).ToList();
My Goal
Obviously from my code I want to group by the performance anchor in the association table, but I need more information from the Initial Training table to include in my ViewModel MedicStatistic, but I am having trouble figuring out the best way to do it.
My overall goal is to be able to get the most recent time a performance anchor was completed from the Initial Training table.
Visual
Initial Training Table (not all fields were captured in snippet b/c they're not important for the purpose of this question)
Initial Training Association Table
What I expect
So, from the pictures provided above as you can see there are multiple 1's for performance anchor id's in the association table, but they each have different InitialTrainingId. So, this specific performance anchor has been done multiple times, but I need to get the most recent date from the Initial Training table. Also, I need to get the corresponding grade with the anchor from the Grading System table, based on the most recent date.
So, for the performance anchor that equals 1.. I would want the grade that corresponds to the InitialTrainingId of 17 because that record was the most recent time that the performance anchor of 1 was done.
If you have any questions please let me know.
You want the data grouped by CodePerformanceAnchor, so the most natural way to start the query is at its DbSet which immediately eliminates the necessity of grouping:
from pa in db.CodePerformanceAnchors
let mostRecentInitialTraining
= pa.InitialTrainingAssociations
.Select(ita => ita.InitialTraining)
.OrderByDescending(tr => tr.DateTakenInitial)
.FirstOrDefault()
select new
{
pa.PerformanceAnchor,
mostRecentInitialTraining.DateTakenInitial,
mostRecentInitialTraining. ...
...
AnchorCount = pa.InitialTrainingAssociations.Count()
}
As you see, only navigation properties are used and the query as a whole is pretty straightforward. I assume that the PerformanceAchor class also has an InitialTrainingAssociations collection.
I can't guarantee that EF will be able to execute it entirely server-side though, that's always tricky with more complex LINQ queries.
I'm going to ignore the virtual properties in your InitialTrainingAssociation class, since you didn't mention anything about them and it's not immediately apparent to me whether they actually contain data, or why they are virtual.
It seems like IQueryable.Join is the easiest way to combine the data you want.
In the following example, we will start with the entries from the InitialTrainings table. We will then Join with the InitialTrainingAssociations table, which will result in a collection of paired InitialTraining and InitialTrainingAssociation objects.
var initialTrainingResults =
// Start with the InitialTrainings data.
db.InitialTrainings
// Add association information.
.Join(
// The table we want to join with
db.InitialTrainingAssociations,
// Key selector for the outer type (the type of the collection
// initiating the join, in this case InitialTraining)
it => it.Id,
// Key selector for the inner type (the type of the collection
// being joined with, in this case InitialTrainingAssociation)
ita => ita.InitialTrainingId,
// Result selector. This defines how we store the joined data.
// We store the results in an anonymous type, so that we can
// use the intermediate data without having to declare a new class.
(InitialTraining, InitialTrainingAssociation) =>
new { InitialTraining, InitialTrainingAssociation }
)
From here, we can add data from the PerformanceAnchors and GradingSystems tables, by performing more Joins. Each time we perform a Join, we will add a new entity to our anonymous type. The result will be a collection of anonymous types representing data we retrieved from the database.
// Add performance anchor information.
.Join(
db.PerformanceAnchors,
x => x.InitialTrainingAssociation.PerformanceAnchorId,
pa => pa.Id,
(x, PerformanceAnchor) =>
new { x.InitialTrainingAssociation, x.InitialTraining, PerformanceAnchor }
)
// Add grading system information.
.Join(
db.GradingSystems,
x => x.InitialTrainingAssociation.GradingSystemId,
gs => gs.Id,
// No need for InitialTrainingAssociation anymore, so we don't
// include it in this final selector.
(x, GradingSystem) =>
new { x.InitialTraining, x.PerformanceAnchor, GradingSystem }
);
(This was a verbose example to show how you can join all the tables together. You can use less Joins if you don't need to access all the data at once, and you can filter down the InitialTrainings collection that we start with if you know you only need to access certain pieces of data.)
At this point, initialTrainingResults is an IEnumerable containing one entry for each association between the InitialTrainings, PerformanceAnchors, and GradingSystems tables. Essentially, what we've done is taken all the InitialTrainingAssociations and expanded their Ids into actual objects.
To get the most recent set of data for each performance anchor:
var performanceAnchors = initialTrainingResults
// Group by each unique Performance Anchor. Remember, the IEnumerable
// we are operating on contains our anonymous type of combined Training,
// Performance Anchor and Grading data.
.GroupBy(x => x.PerformanceAnchor.Id)
// Order each Performance Anchor group by the dates of its training,
// and take the first one from each group
.Select(g => g.OrderByDescending(x => x.InitialTraining.DateTakenInitial).First());
In the Select you can order the group result to get the most recent associated InitialTraining by DateTakenInitial, and from there get the desired data
//...omitted for brevity
.GroupBy(t => t.PerformanceAnchorId)
.Select(g => {
var mostRecent = g.OrderByDescending(_ => _.InitialTraining.DateTakenInitial).First();
// get the corresponding grade with the anchor from the Grading System table
var gradeid = mostRecent.GradingSystemId;
var gradingSystem = mostRecent.GradingSystem;
//get the most recent date from the Initial Training
var mostRecentDate = mostRecent.InitialTraining.DateTakenInitial
//..get the desired values and assign to view model
var model = new MedicStatistic {
//Already have access to CodePerformanceAnchor
PerformanceAnchorName = mostRecent.CodePerformanceAnchor.PerformanceAnchor
AnchorCount = g.Count(),
MostRecentlyCompleted = mostRecentDate,
};
return model;
});
How can the following be accomplished using LINQ
SELECT r.BrandID
FROM dbo.Items AS r
JOIN Brands AS d ON r.BrandID = d.BrandID
WHERE CategoryID IN (SELECT CategoryID
FROM dbo.Categories
WHERE Name = 'Bread - Bakery')
Code for Brand class:
public class Brand
{
public int BrandID { get; set; }
[DisplayName("Brand Name")]
public string Name { get; set; }
public virtual List<Category> Categories { get; set; }
public virtual List<Item> Items { get; set; }
}
Code for Item class:
public class Item
{
[Key]
public int ItemID { get; set; }
public virtual Category Category { get; set; }
public virtual Brand Brand { get; set; }
public int CategoryID { get; set; }
public int BrandID { get; set; }
}
code for Category class:
public class Category
{
[Key]
public int CategoryID { get; set; }
[DisplayName("Category Name")]
public virtual string Name { get; set; }
public virtual List<Brand> Brands { get; set; }
public virtual List<Item> Items { get; set; }
}
dbContext.Items
.Where(x => x.Category.Name.Equals("Bread - Bakery"))
.Select(x => x.BrandID);
I am not sure why you need to use below join. It seems that it is not needed (unless intentionally inner joined with brands to remove non-matching records from items)
JOIN Brands AS d ON r.BrandID = d.BrandID
Hm, pity you didn't write your requirements, now I have to guess what they are from your SQL code.
So you have a database with Brands, Items and Categories. Every Item has a Category, every Category can be used by zero or more Items: a one-to-many relation
Every Item is of a certain Brand, Every Brand can have zero or more items: also a straightforward one-to-many relation.
Finally every Brand has zero or more Categories, every Category has zero or more Brands: many-to-many
Now you take your collection of Items, you only want to keep those Items that have a Category with a Name that equals Bread - Bakery. From the remaining items you want all their BrandIds.
The requirement would be: "Give me the BrandIds of all Items that have a Category with a Name that equals 'Bread - Bakery`.
If you use entity framework, it is usually easier if you use the virtual ICollection instead of doing the join yourself. Entity framework knows the relations between the tables and will compose the proper joins for it.
var result = myDbContext.Items // from the collection of Items
.Where(item => item.Category.Name == "Bread - Bakery") // keep only those with a Category
// that has a Name equal to ...
.Select(item.BrandId); // from the remaining items select the BrandId
If you really want, and you can convince your project leader that entity framework can't be trusted to do the proper joins you can do the join yourself:
// get the sequence of categories that I'm interested in:
var breadBakeryCategories = myDbContext.Categories
.Where(category => category.Name == "Bread - Bakery");
// join the items with these categories
// and select the BrandIds
var requestedBrandIds= myDbContext.Items
.Join(breadBakeryCategories,
item => item.CategoryId, // from every Item take the CategoryId,
category => category.CategoryId, // from every Category take the CategoryId
(item, category) => item.BrandId); // when they match, select the BrandId
TODO: consider concatenating this into one big ugly LINQ statement.
Remark 1
You do realize that your result might have the same BrandIds several times, don't you?
If you don't want that, start with the Brands:
var result = myDbContext.Brands
.Where(brand => brand.Items.Select(item => item.Category.Name)
.Where(name => name == "Bread - Bakery")
.Any())
.Select(brand => brand.brandId);
In words: from the collection of Brands, keep only those Brands that have at least one Category with a name equal to "Bread - Bakery". From the remaining Brands select the BrandId.
** Remark 2 **
Why are your one-to-many Lists instead of ICollections? Are you sure that brand.Categories[4] has a proper meaning?
var result = myDbContext.Brands
.Where(brand => brand.Category[4].Name == "Bread - Bakeries");
Your compiler won't complain, but you'll get runtime errors.
Consider using virtual ICollection<...> for your one-to-many and many-to-many relations. This way you'll have exactly the functionality you expect with a database table, and your compiler will complain if you try to use functionality that can't be translated into SQL
I have a model in Entity Framework Core that goes something like this:
public class Anime
{
public int EpisodeCount { get { return Episodes.Count() } }
public virtual ICollection<Episode> Episodes { get; set; }
}
I'm having the issue of EpisodeCount being 0. The solution currently is to run a .Include(x => x.Episodes) within my EF query, but that loads the entire collection of episodes where it's not needed. This also increases my HTTP request time, from 100ms to 700ms which is just not good.
I'm not willing to sacrifice time for simple details, so is there a solution where I can have EF only query the COUNT of the episodes, without loading the entire collection in?
I was suggested to do this
var animeList = context.Anime.ToPagedList(1, 20);
animeList.ForEach(x => x.EpisodeCount = x.Episodes.Count());
return Json(animeList);
but this also returns 0 in EpisodeCount, so it's not a feasible solution.
You need to project the desired data into a special class (a.k.a. ViewModel, DTO etc.). Unfortunately (or not?), in order to avoid N + 1 queries the projection must not only include the count, but all other fields as well.
For instance:
Model:
public class Anime
{
public int Id { get; set; }
public string Name { get; set; }
// other properties...
public virtual ICollection<Episode> Episodes { get; set; }
}
ViewModel / DTO:
public class AnimeInfo
{
public int Id { get; set; }
public string Name { get; set; }
// other properties...
public int EpisodeCount { get; set; }
}
Then the following code:
var animeList = db.Anime.Select(a => new AnimeInfo
{
Id = a.Id,
Name = a.Name,
EpisodeCount = a.Episodes.Count()
})
.ToList();
produces the following single SQL query:
SELECT [a].[Id], [a].[Name], (
SELECT COUNT(*)
FROM [Episode] AS [e]
WHERE [a].[Id] = [e].[AnimeId]
) AS [EpisodeCount]
FROM [Anime] AS [a]
I cannot wrap my head around how to write a linq query against my EF context to get what I want.
1) What I have
Database with no foreign keys assigned, and a reverse engineered code first entity framework project. I tried manually adding virtual classes so EF might create implied foreign keys in the DBcontext, but I get errors on my .Include statements still.
Without the include the only thing I can think of is to use left joins, but I haven't gotten it down yet. In the end there will be 21 tables I have to get data from, but the following table outline encapsulates the majority of issues i'm facing.
Sample data structure:
Table Human: HumanId, LastFoodEatenId, FavoriteFoodId, CurrentlyDesiredFoodId
Table Food: FoodId, FoodName, FoodStuff
Table Toys: HumanOwnerId, ToyId, ToyName
Table Pets: HumanOwnerId, PetId, PetName, PetType
Table PetSurgery: PetId, SurgeryId, SurgeryPerformed
2) What I want
Given a HumanID, I want a compsite class or something like it from a single query.
Public Class QueryResult
{
public Human human {get;set;}
public Food LastEatenFood {get;set;}
public Food FavoriteFood {get;set;}
public Food CurrentlyDesiredFood {get;set;}
public IEnumerable<Toy> Toys {get;set;}
public IEnumerable<Pet> Pets {get;set;} //Includes surgeries if any
}
Is it even possible to write a single query to get this kind of information in a single db hit? I'd be fine is someone simply confirmed it is't possible. Then I can at least request we add relationships to our database.
Thanks in advance,
You can use linq to query multiple, non-related tables.
I'm going to assume a LOT about your entities, but here we go...
int humanId = 1234;
using (var context = new MyContext())
{
var human = (from h in context.Humans
join lf in context.Foods on h.LastFoodEatenId equals lf.foodId into lfg
from lf in lfg.DefaultIfEmpty() // left join
join ff in context.Foods on h.FavoriteFoodId equals lf.foodId into ffg
from ff in ffg.DefaultIfEmpty() // left join
join cf in context.Foods on h.CurrentlyDesiredFoodId equals lf.foodId into cfg
from cf in cfg.DefaultIfEmpty() // left join
join p in context.Pets on h.humanId equals p.humanId into pg // group
join t in context.Toys on h.humanId equals t.humanId into tg // group
where h.humanId = humanId
select new QueryResult { human = h, LastEatenFood = lf, FavoriteFood = ff, CurrentlyDesiredFood = cf, Toys = tg, Pets = pg }
).SingleOrDefault();
}
Note: I'm doing this from memory without a syntax checker, so ymmv. Adding surgeries should be possible as well, but may require a subquery.
I tried manually adding virtual classes
I assume you mean virtual collections. You can define relationships in a "code-first" model if they are not in the database. The only condition is that foreign keys must refer to properties that EF knows as primary keys. So you should be able to do LINQ queries using navigation properties in stead of these verbose joins by a model like this (reduced to the essentials):
class Human
{
public int HumanId { get; set; }
public int LastFoodEatenId { get; set; }
public virtual Food LastEatenFood { get; set; }
public int FavoriteFoodId { get; set; }
public virtual Food FavoriteFood { get; set; }
public int CurrentlyDesiredFoodId { get; set; }
public virtual Food CurrentlyDesiredFood { get; set; }
public virtual ICollection<Toy> Toys { get; set; }
public virtual ICollection<Pet> Pets { get; set; }
}
class Food
{
public int FoodId { get; set; }
}
class Pet
{
public int PetId { get; set; }
public int HumanOwnerId { get; set; }
}
class Toy
{
public int ToyId { get; set; }
public int HumanOwnerId { get; set; }
}
And a mapping:
class HumanMapping : EntityTypeConfiguration<Human>
{
public HumanMapping()
{
HasOptional(h => h.LastEatenFood).WithMany()
.HasForeignKey(h => h.LastFoodEatenId);
HasOptional(h => h.FavoriteFood).WithMany()
.HasForeignKey(h => h.FavoriteFoodId);
HasOptional(h => h.CurrentlyDesiredFood).WithMany()
.HasForeignKey(h => h.CurrentlyDesiredFoodId);
HasMany(h => h.Toys).WithOptional().HasForeignKey(t => t.HumanOwnerId);
HasMany(h => h.Pets).WithOptional().HasForeignKey(t => t.HumanOwnerId);
}
}
EF will infer the primary keys by name conventions.
Now you will be able to execute a LINQ statement like:
context.Humans.Where(h => h.HumanId == id)
.Include(h => h.LastEatenFood)
.Include(h => h.FavoriteFood)
.Include(h => h.CurrentlyDesiredFood)
.Include(h => h.Toys)
.Include(h => h.Pets)
From your description I understand that PetSurgery should be a junction class between Pet and another class (Surgery?). Anyway, I think you will manage creating the correct mappings, seeing this example.