I have the following models:
public class Order
{
public int Id {get; set;}
public int CustomerId {get; set;}
public virtual Category Category {get; set;}
//Many more properties...
}
public class OrderLine
{
public int Id {get; set;}
public int OrderId {get; set;}
public virtual Order Order {get; set;}
public virtual Product Product {get; set;}
//Other properties...
}
I need to get the orders of a particular customer. In order not to retrieve too many information, I created a class:
public class CustomerOrder
{
public int CustomerId {get; set;}
public int OrderId {get; set;}
public string ProductName {get; set;}
public virtual ICollection<OrderLine> {get; set;}
}
I have mapping configuration for the Order and OrderLine classes but none for CustomerOrder as I was thinking that I can project data into this class.
I can:
Use EF to retrieve the data by specifying includes. After the data is retrieved I can project it into the CustomerOrder class. However, will this force EF to retrieve all columns for the main and included tables?
Use a custom SQL query to retrieve the required details from the Order table (maybe directly from a view). The use Linq to join this resultset with OrderLine to have the complete projection. However, will I need to have mapping configuration for the view?
To avoid too many columns and join in the SQL select statement, what is the best way to project the data into CustomerOrder?
You can do it as shown below.You have to do some changes on your models as well.I have done that.Please see that too.
public class Order
{
public int Id {get; set;}
public int CustomerId {get; set;}
public virtual Category Category {get; set;}
public virtual ICollection <OrderLine> OrderLines {get; set;}
//Many more properties...
}
public class OrderLine
{
public int Id {get; set;}
public int OrderId {get; set;}
public virtual Order Order {get; set;}
public virtual Product Product {get; set;}
//Other properties...
}
public class CustomerOrder
{
public int CustomerId {get; set;}
public int OrderId {get; set;}
public string ProductName {get; set;}
public virtual ICollection<OrderLine> OrderLines {get; set;}
}
Final Query :
var orderList = (from order in _context.Orders
from orderLine in order.OrderLines)
select new CustomerOrder
{
CustomerId = order.CustomerId,
OrderId = orderLine.OrderId,
ProductName= orderLine.Product.ProductName,
OrderLines = order.OrderLines
}).AsNoTracking().ToList();
A 1 : No.Only the projected columns will be fetched from the db.
Best Approach : Always use the custom projection (like CustomerOrder).That is the best when we consider the Performance of the EF query.You can use that to send data to the View too (it's like a DTO (Data Transfer Object)).
Related
I am working on a project which involves EF Core.
I would like to use the foreign keys from Category with one single navigation property.
Therefore, Item stores the foreign keys of Category, and the names of the Category can be shown.
This is how the relationship looks like:
Classes:
[Table("Item" , Schema = "public")]
public class Item
{
[Key]
[DatabaseGenerated(DatabaseGeneratedOption.Identity)]
public int ItemID {get; set;}
public string Name {get; set;}
public int CategoryID {get; set;}
//Single Navigation Property
public Category Category {get; set;}
}
[Table("Category" , Schema = "public")]
public class Category
{
[Key]
[DatabaseGenerated(DatabaseGeneratedOption.Identity)]
public int CategoryID {get; set;}
public string Name {get; set;}
}
DbContext:
protected override void OnModelCreating(ModelBuilder modelBuilder)
{
modelBuilder.Entity<Item>().ToTable("Item");
modelBuilder.Entity<Category>().ToTable("Category");
modelBuilder.Entity<Item>()
.HasOne(i=>i.Category)
.WithOne()
.HasForeignKey<Item>(i=>i.CategoryID);
}
It shows an error
Duplicate key value violates unique constraint "IX_ItemDB_CategoryID"
Apparently, it means CategoryID cannot be duplicate in Item.
What am I doing wrong here? Thanks!
actually your answer in this article. What you need to do is change the location of the navigation property. So Item should not have an Category property, Category should have a collection of Item for single navigation. the article describes other ways.
In case I understand properly You need one to many relation and I can offer you that structure and if you use Migration your tables will be properly build in the database. No to do anything in the FluentApi to, Your FK, PK(identity) and Indexes will be automatically created
[Table("Item" , Schema = "public")]
public class Item
{
public int Id {get; set;}
public string Name {get; set;}
public int CategoryId {get; set;}
public Category Category {get; set;}
}
[Table("Category" , Schema = "public")]
public class Category
{
public Category()
{
this.Items = new HashSet<Item>();
}
public int Id {get; set;}
public string Name {get; set;}
public virtual ICollection<Item> Items {get; set;}
}
Ivan Stoev is correct. The model of my question is fine and fluent configurations are not required. EFCore will handle the rest.
Hi I have a simple database, and what I am trying to do is build simple include maps as string using eager loading mechanism in EF CORE.
So in other words mu db models looks like:
And models that are supporting them:
public class StartTable
{
public int Id {get; set;}
public ICollection<TableA> TableA {get; set;}
public ICollection<TableB> TableA {get; set;}
}
public class TableA
{
public int Id {get; set;}
public StartTable StartTable {get; set;}
public int StartTableId {get; set;}
public TableAChild TableAChild {get; set;}
public int TableAChildId {get; set;}
public TableAB TableAB {get; set;}
public int TableABId {get; set;}
}
public class TableB
{
public int Id {get; set;}
public StartTable StartTable {get; set;}
public int StartTableId {get; set;}
public TableBChild TableBChild {get; set;}
public int TableBChildId {get; set;}
public TableAB TableAB {get; set;}
public int TableABId {get; set;}
}
public class TablAChild
{
public int Id {get; set;}
public TableA TableA {get; set;}
}
public class TableBChild
{
public int Id {get; set;}
public TableB TableB {get; set;}
}
public class TableAB
{
public int Id {get; set;}
public TableA TableA {get; set;}
public TableB TableB {get; set;}
}
I think relations are readible from models. Now I just want to create a map, that is I want to select start table and with include of all branches so final include path should looks like:
_context.StartTable.Include("StartTable.TableA.TableAChild")
_context.StartTable.Include("StartTable.TableA.TableAB")
_context.StartTable.Include("StartTable.TableB.TableBChild")
_context.StartTable.Include("StartTable.TableB.TableAB")
And If I type this manually it works, but this will grow a lot so I don't want to update this every time something will come up, I tried AutoInclute() in context on main table but it includes only 1 level down.
I thought I can create some sort of map function that looks like:
private static IEnumerable<string> BuildIncludeTree(DbContext context, Type type)
{
var entityAssemblyTypes = Assembly.GetExecutingAssembly().GetReferencedAssemblies().SelectMany(assembly => Assembly.Load(assembly).GetTypes());
void AddAssetByString(ref HashSet<string> navigation, List<string> createdPaths)
{
foreach (var path in createdPaths)
{
var splitPath = path.Split('.');
var relationNavigationNode = splitPath.Last();
var parentNavigationType = entityAssemblyTypes.FirstOrDefault(t => t.Name == relationNavigationNode);
if (parentNavigationType == null)
{
throw new ArgumentException($"Unknown type parent: {relationNavigationNode}");
}
var parentNodesProperties =
parentNavigationType.GetProperties().Where(prop => !prop.PropertyType.IsSimple() && !splitPath.Contains(prop.Name)).ToArray();
if (!parentNodesProperties.Any())
{
navigation.Add(path);
continue;
}
navigation.Add(path);
AddAssetByString(ref navigation, parentNodesProperties.Select(prop => $"{path}.{prop.Name}").ToList());
}
}
IEntityType entityType = context.Model.FindEntityType(type);
if (entityType == null) throw new ArgumentException($"Unknown entity type {type.Name}");
var navigationsByString = new HashSet<string>();
var relationsByString = entityType.GetNavigations().Select(nav => $"{type.Name}.{nav.Name}");
AddAssetByString(ref navigationsByString, relationsByString.ToList());
return new List<string>();
}
But problem here is relation to TableAB, I mean when I get to mapping this part function goes circular and creates map:
StartTable.TableA.TableAChild.TableB.StartTable.TableA ... and so on
Can this be prevented and what am I missing?
Can EF Core detect in some sort of way navigation downwards and upwards?
Or is there any other and simpler way to do that?
You can't Include all .There is already post about that here
Is there a way to Include() all with dbcontext?
But if correctly understand you can use Linq to make you code shorter like:
_context.StartTable.Include(x => x.TableA.TableAChild && x.TableA.TableAB && x. ....)
And in that case you will need to add entities you want to include in your class also you can use [NotMapped] attribute if you working direct with your class instead of dto. So in that way you can access the mapped entities direct from the class like class.TableAChild
+
public virtual TableAChild TableAChild { get; set; }
public virtual TableAB TableAB { get; set; }
Greetings and good luck
I am trying to work out how to add a reference an object from within EF.
I little hard to explain so I thought I would share a dotnetfiddle example
https://dotnetfiddle.net/4n5Flk
public class ReportConfig
{
[Key]
public int ReportConfigKey {get; set;}
public int ConfigTypeKey {get; set;}
public int ConfigValue {get; set;}
[ForeignKey("ConfigTypeKey")]
public virtual <ConfigType> ConfigType {get; set;}
}
public class ConfigType
{
[Key]
public int ConfigTypeKey {get; set;}
//This can be
//Address
//Car etc etc.
public string ConfigName {get; set;}
}
public class Car
{
[Key]
public int CarId {get; set;}
//other items
}
public class Address
{
[Key]
public AddressId {get; set;}
}
In a nutshell I am trying to create a navigation property to either a car or an address based on the ConfigValue and the ConfigTypeKey
I was thinking to create 2 navigation properties "Car" and "Address" and for both add 2 foreign key's 1 to the object and 1 as a hardcoded reference to ConfigName as Car or Address
is this possible atall
Sorry for the poor explanation.
Assume following model
class Order()
{
public int Id {get; set;}
public List<OrderItem> Items {get; set;}
}
class OrderItem()
{
public int Id {get; set;}
public string Name {get; set;}
}
So I have an order that has 10 items, now I need to build a query that returns all Orders that have the last item in their collection property Items having Name equals to specific value. How do I do that?
How can i add a foreign key to a Model (code first)
i have a model Product which has an ID (primary key) which i want to add to my model order like.
public class Order
{
public int ID {get; set;}
[Required]
public int Total {get; set;}
[Required]
public int ProductId{get; set;}
}
but how can i make the ProductId refer to the id of my Product model like a foreign key?
On Stackoverflow there are alot simmilar questions but all with different answers, but they arent working for me. I really hope someone has a solution or can points me in the right direction with an explanation.
You need to add a navigation property:
public virtual Product Product { get; set; }
So the Order class will look like this:
public class Order
{
public int ID {get; set;}
[Required]
public int Total {get; set;}
[Required]
public int ProductId{get; set;}
[Required]
public virtual Product Product { get; set; }
}
Also, strictly speaking the ProductId property isn't needed once you have the virtual Product property.
You could do something like this:
public class Order
{
public int ID {get; set;}
[Required]
public int Total {get; set;}
[Required]
public int ProductId{get; set;}
[ForeignKey("ProductId")]
public virtual Product Product {get; set;}
}