I am using RavenDb in C# web project. I have an object that I need to query its child collection with 1 row per child object and some of the root/parent object properties.
Note: This is not the actual design, just simplified for this question.
public class OrderLine
{
public string ProductName { get; set; }
public int Quantity { get; set; }
public DateTime? ShipDate { get; set; }
}
public class Order
{
public int OrderId { get; set; }
public string CustomerName { get; set; }
public DateTime OrderDate { get; set; }
public List<OrderLine> OrderLines { get; set; }
}
The order with the orderlines is one single document. ShipDate will be updated on each line because not all products are always in stock.
I need to be able to create a list of the last 10 products sent with the following columns:
OrderId
Customer
ProductName
ShipDate
This doesn't work because SelectMany is not supported:
var query = from helper in RavenSession.Query<Order>()
.SelectMany(l => l.OrderLines, (order, orderline) =>
new { order, orderline })
select new
{
helper.order.OrderId,
helper.order.CustomerName,
helper.orderline.ProductName,
helper.orderline.ShipDate
};
var result = query.Where(x => x.ShipDate.HasValue)
.OrderByDescending(x => x.ShipDate.Value).Take(10);
I believe the right thing to do isto create an Index that will flatten out the list but I haven't had any success. I don't believe a Map-Reduce situation will work because as I understand it will effectively does a group by which Reduces the number of documents to less rows (in the index). But in this case, I am trying to expand the number of documents to more rows (in the index).
I would rather not put each OrderLine in a separate document but I do not know what my options are.
Since you want to filter and sort by fields in the subclass, you'll need to make sure all the fields you want are indexed and stored.
public class ShippedItemsIndex
: AbstractIndexCreationTask<Order, ShippedItemsIndex.Result>
{
public class Result
{
public int OrderId { get; set; }
public string CustomerName { get; set; }
public string ProductName { get; set; }
public int Quantity { get; set; }
public DateTime ShipDate { get; set; }
}
public ShippedItemsIndex()
{
Map = orders =>
from order in orders
from line in order.OrderLines
where line.ShipDate != null
select new
{
order.OrderId,
order.CustomerName,
line.ProductName,
line.Quantity,
line.ShipDate
};
StoreAllFields(FieldStorage.Yes);
}
}
Then you can project from the index into your results.
var query = session.Query<Order, ShippedItemsIndex>()
.ProjectFromIndexFieldsInto<ShippedItemsIndex.Result>()
.OrderByDescending(x => x.ShipDate)
.Take(10);
var results = query.ToList();
Here is a complete test demonstrating.
Related
Not sure if i worded the question correctly, but what im trying to do is return a new viewmodel with one of the parts being a booking:
public class Booking
{
public int BookingId { get; set; }
public int CustomerId { get; set; }
public Guid UniqueId { get; set; }
public string EventId { get; set; }
public bool IsPaid { get; set; }
public double Price { get; set; }
public DateTime BookingDate { get; set; }
public DateTime DateBooked { get; set; }
[JsonIgnore]
public Customer Customer { get; set; }
[JsonIgnore]
public ICollection<BookingService> BookingServices { get; set; }
[NotMapped]
public IEnumerable<Service> Services { get; set; }
}
and my query is:
var customers = _dbContext.Customers
.Select(c => new CustomerBookingsViewModel
{
Customer = c,
Bookings = c.Bookings.Select(b => new Booking
{
BookingId = b.BookingId,
BookingDate = b.BookingDate,
DateBooked = b.DateBooked,
CustomerId = b.CustomerId,
UniqueId = b.UniqueId,
EventId = b.EventId,
IsPaid = b.IsPaid,
Price = b.Price,
Services = b.BookingServices.Select(s => s.Service)
}),
}
)
.ToList();
What I want to know is how to I select all the booking info into the booking without selecting each part, ie:
BookingId = b.BookingId,
BookingDate = b.BookingDate,
DateBooked = b.DateBooked,
CustomerId = b.CustomerId,
UniqueId = b.UniqueId,
EventId = b.EventId,
IsPaid = b.IsPaid,
Price = b.Price,
Can it be done or because the list of services is inside the booking model it cant?
Thanks.
You could implement the IClonable interface on your class.
public class MyClass : ICloneable
{
public int Id { get; set; }
public object Clone() => MemberwiseClone();
}
Usage:
var list1 = new List<MyClass>
{
new MyClass() { Id = 2 },
new MyClass() { Id = 5 }
};
var list2 = list1.Select(x => (MyClass)x.Clone()).ToList();
list2.First().Id = 10; //list1 won't be affected
You should use AutoMapper here to avoid writing each path.
https://automapper.org/
http://docs.automapper.org/en/stable/Getting-started.html
There is no other way, at least it is not related to LINQ or queries.
The question "How to clone an object" has been answered here:
Creating a copy of an object in C#
There is no LINQ way to do this. I would suggest using custom Attribute marking every property you want to copy. This would help if you want not to copy the whole object but some properties. After marking every property you need you can just set the marked props with reflection from one of the objects to the other.
I have the following database entity containing ingredients to put on pizza. Column Type is a foreign key to another table containing information on the ingredient category (cheese, meat, vegetables etc.)
public class Ingredient
{
public int IngredientId { get; set; }
public string Name { get; set; }
public bool IsVegetarian { get; set; }
public int Type { get; set; }
}
Some sample data:
sample ingredients
For each unique 'Type' value, I want to return a List of Ingredients with that type.
The final result will be stored in an ICollection of type IngredientViewModel.
public class IngredientViewModel : Model
{
public IngredientCategory Category { get; set; }
public List<Ingredient> Ingredients { get; set; }
}
How can I best get all ingredients, grouped per category in a single database trip using linq or lambda expressions?
I currently have the following snippet which I find a bit messy:
public async Task<IEnumerable<IngredientViewModel>> GetIngredientsPerCategoryAsync()
{
IEnumerable<Ingredient> result = await _repo.GetAllAsync();
IEnumerable<IngredientViewModel> viewModels = result.GroupBy(
x => x.Type,
(category, ingredients) => new IngredientViewModel()
{
Category = (IngredientCategory)category,
Ingredients = MapFromEntities(ingredients)
})
.OrderBy(x => x.Category.ToString())
.ToList();
return viewModels;
}
The most obvious would be: Ingredients = g.ToList().
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 am trying to get the average rating of all restaurants and return the names of all resteraunts associated with that id, I was able to write a sql statement to get the average of restaurants along with the names of the restaurants however I want to only return the name of the restaurant once.
Select t.Average, Name from [dbo].[Reviews] as rev
join [dbo].[Resteraunts] as rest
on rest.ResterauntId = rev.ResterauntId
inner join
(
SELECT [ResterauntId],
Avg(Rating) AS Average
FROM [dbo].[Reviews]
GROUP BY [ResterauntId]
)
as t on t.ResterauntId = rest.ResterauntId
resteraunt class
public int ResterauntId { get; set; }
public string Name { get; set; }
public string Address { get; set; }
public string City { get; set; }
public virtual ICollection<Review> Reviews { get; set; }
public virtual Review reviews{ get; set; }
Review class
public int ReviewId { get; set; }
public double Rating { get; set; }
[ForeignKey("ResterauntId")]
Resteraunt Resteraunt { get; set; }
public int ResterauntId { get; set; }
public DateTime DateOfReview { get; set; }
If possible I would like to have the answer converted to linq.
Resteurants.Select(r => new {
Average = r.Reviews.Average(rev => rev.Rating),
r.Name
})
This should give you a set of objects that have Average (the average of all reviews for that restaurant) and the Name of the restaurant.
This assumes that you have correctly setup the relationships so that Restaurant.Reviews only refers to the ones that match by ID.
If you don't have that relationship setup and you need to filter it yourself:
Resteurants.Select(r => new {
Average = Reviews.Where(rev => rev.ResteurantId == r.Id).Average(rev => rev.Rating),
r.Name
})
Firstly your models seems to have more aggregation than required, I have taken the liberty to trim it and remove extra fields, ideally all that you need a Relation ship between two models RestaurantId (Primary Key for Restaurant and Foreign Key (1:N) for Review)
public class Restaurant
{
public int RestaurantId { get; set; }
public string Name { get; set; }
public string Address { get; set; }
public string City { get; set; }
public virtual ICollection<Review> Reviews { get; set; }
}
public class Review
{
public int ReviewId { get; set; }
public double Rating { get; set; }
public int RestaurantId { get; set; }
public DateTime DateOfReview { get; set; }
}
If these are the models, then you just need List<Restaurant> restaurantList, since that internally contains the review collection, then all that you need is:
var result =
restaurantList.Select(x => new {
Name = x.Name,
Average = x.Reviews.Average(y => y.Rating)
}
);
In case collection aggregation is not there and you have separate ReviewList as follows: List<Review> reviewList, then do the following:
var result =
reviewList.GroupBy(x => x.RestaurantId, x => new {x.RestaurantId,x.Rating})
.Join(restaurantList, x => x.Key,y => y.RestaurantId,(x,y) => new {
Name = y.Name,
AvgRating = x.Average(s => s.Rating)
});
Also please note this will only List the Restaurants, which have atleast one review, since we are using InnerJoin, otherwise you need LeftOuterJoin using GroupJoin, for Restaurants with 0 Rating
I see your Restaurant class already has an ICollection<Review> that represents the reviews of the restaurant. This is probably made possible because you use Entity Framework or something similar.
Having such a collection makes the use of a join unnecessary:
var averageRestaurantReview = Restaurants
.Select(restaurant => new
.Where(restaurant => ....) // only if you don't want all restaurants
{
Name = restaurant.Name,
AverageReview = restaurants.Reviews
.Select(review => review.Rating)
.Average(),
});
Entity Framework will do the proper joins for you.
If you really want to use something join-like you'd need Enumerable.GroupJoin
var averageRestaurantReview = Restaurants
.GroupJoin(Reviews, // GroupJoin Restaurants and Reviews
restaurant => restaurant.Id, // From every restaurant take the Id
review => review.RestaurantId, // From every Review take the RestaurantId
.Select( (restaurant, reviews) => new // take the restaurant with all matching reviews
.Where(restaurant => ....) // only if you don't want all restaurants
{ // the rest is as before
Name = restaurant.Name,
AverageReview = reviews
.Select(review => review.Rating)
.Average(),
});
I have a Comment and Votes related to the comment.
[Table("QAComment")]
public class QaComment : IEntity
{
[Key, Column("QACommentID")]
public int Id { get; set; }
// ...
public virtual ICollection<QaCommentVote> Votes { get; set; }
[NotMapped]
public int OverallVote { get; set; }
}
[Table("QACommentVote")]
public class QaCommentVote : IEntity
{
[Key, Column("QACommentVoteID")]
public int Id { get; set; }
[ForeignKey("QAComment")]
public int QaCommentId { get; set; }
public int Value { get; set; }
public virtual QaComment QaComment { get; set; }
}
I need to get comments with the sum of their votes, not pulling all votes to the application.
The ways I can see to achive this:
1. Make a database view for Commment and calc votes sum in there.
Cons: dont wanna make extra-views
2. Via LINQ:
var comments =
Set<QaComment>()
.Select(c => new QaComment() {/* assign every property once again and calc OverallVote */});
Cons: don't like to assign allproperties once again.
Is there a better way devoid of that cons?
UPDATE
This is what I want as a result of LINQ:
SELECT
qac.*,
(SELECT SUM(v.Value)
FROM QACommentVote v
WHERE v.QACommentID = qac.QACommentID) as OverallVote
FROM QAComment qac
You can fetch QaComment and the sum you're looking for separately as anonymous type and merge them into one object using LINQ to Objects:
var comments
= Set<QaComment>()
.Select(c => new { c, sum = c.Votes.Sum(v => v.Value))
.AsEnumerable() // to make next query execute as LINQ to Objects query
.Select(x => { x.c.OverallVote = x.sum; return x.c; })
.ToList();
But to make point clear: I haven't tested that :)