I am new to EF and i have the following scenario:
I want to load the IHave apples without loading the whole Apples collection.
The model:
public class Category
{
public virtual ICollection<Classified> Apples { get; set; }
[NotMapped]
public bool IHaveApples {get { return Apples.count > 0; } }
}
And the FLUENT API Config:
public class CategoryConfiguration : EntityTypeConfiguration<Category>
{
public CategoryConfiguration()
{
HasMany(o => o.Apples ).WithRequired().HasForeignKey(o => o.CategoryId);
}
}
And in my controller i go with
//The controller returns IQueryable<Category>
var category = _contextProvider.Context.Categories;
Thanks in advance,
Stelios K.
As IHaveApples is a bool, you should simply use Apples.Any() instead of Count.
EDIT:
If you want this to be automatically set (i.e. the boolean is set without even accessing manually to your collection), what you could do is add an handler to the ObjectMaterialized event:
public class Category
{
...
public bool IHaveApples { get; set; }
}
((IObjectContextAdapter)yourDbContext).ObjectContext.ObjectMaterialized += (sender, e) =>
{
var entityAsCategory = e.Entity as Category;
if (entityAsCategory != null)
{
entityAsCategory.IHaveApples = yourDbContext
.Entry(entityAsCategory)
.Collection(z => z.Apples)
.Query()
.Any();
}
};
Related
I am using EF Core 3.1.7. The DbContext has the UseLazyLoadingProxies set. Fluent API mappings are being used to map entities to the database. I have an entity with a navigation property that uses a backing field. Loads and saves to the database seem to work fine except for an issue when accessing the backing field before I access the navigation property.
It seems that referenced entities don't lazy load when accessing the backing field. Is this a deficiency of the Castle.Proxy class or an incorrect configuration?
Compare the Student class implementation of IsRegisteredForACourse to the IsRegisteredForACourse2 for the behavior in question.
Database tables and relationships.
Student Entity
using System.Collections.Generic;
namespace EFCoreMappingTests
{
public class Student
{
public int Id { get; }
public string Name { get; }
private readonly List<Course> _courses;
public virtual IReadOnlyList<Course> Courses => _courses.AsReadOnly();
protected Student()
{
_courses = new List<Course>();
}
public Student(string name) : this()
{
Name = name;
}
public bool IsRegisteredForACourse()
{
return _courses.Count > 0;
}
public bool IsRegisteredForACourse2()
{
//Note the use of the property compare to the previous method using the backing field.
return Courses.Count > 0;
}
public void AddCourse(Course course)
{
_courses.Add(course);
}
}
}
Course Entity
namespace EFCoreMappingTests
{
public class Course
{
public int Id { get; }
public string Name { get; }
public virtual Student Student { get; }
protected Course()
{
}
public Course(string name) : this()
{
Name = name;
}
}
}
DbContext
using Microsoft.EntityFrameworkCore;
using Microsoft.Extensions.Logging;
namespace EFCoreMappingTests
{
public sealed class Context : DbContext
{
private readonly string _connectionString;
private readonly bool _useConsoleLogger;
public DbSet<Student> Students { get; set; }
public DbSet<Course> Courses { get; set; }
public Context(string connectionString, bool useConsoleLogger)
{
_connectionString = connectionString;
_useConsoleLogger = useConsoleLogger;
}
protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
{
ILoggerFactory loggerFactory = LoggerFactory.Create(builder =>
{
builder
.AddFilter((category, level) =>
category == DbLoggerCategory.Database.Command.Name && level == LogLevel.Information)
.AddConsole();
});
optionsBuilder
.UseSqlServer(_connectionString)
.UseLazyLoadingProxies();
if (_useConsoleLogger)
{
optionsBuilder
.UseLoggerFactory(loggerFactory)
.EnableSensitiveDataLogging();
}
}
protected override void OnModelCreating(ModelBuilder modelBuilder)
{
modelBuilder.Entity<Student>(x =>
{
x.ToTable("Student").HasKey(k => k.Id);
x.Property(p => p.Id).HasColumnName("Id");
x.Property(p => p.Name).HasColumnName("Name");
x.HasMany(p => p.Courses)
.WithOne(p => p.Student)
.OnDelete(DeleteBehavior.Cascade)
.Metadata.PrincipalToDependent.SetPropertyAccessMode(PropertyAccessMode.Field);
});
modelBuilder.Entity<Course>(x =>
{
x.ToTable("Course").HasKey(k => k.Id);
x.Property(p => p.Id).HasColumnName("Id");
x.Property(p => p.Name).HasColumnName("Name");
x.HasOne(p => p.Student).WithMany(p => p.Courses);
});
}
}
}
Test program which demos the issue.
using Microsoft.Extensions.Configuration;
using System;
using System.IO;
using System.Linq;
namespace EFCoreMappingTests
{
class Program
{
static void Main(string[] args)
{
string connectionString = GetConnectionString();
using var context = new Context(connectionString, true);
var student2 = context.Students.FirstOrDefault(q => q.Id == 5);
Console.WriteLine(student2.IsRegisteredForACourse());
Console.WriteLine(student2.IsRegisteredForACourse2()); // The method uses the property which forces the lazy loading of the entities
Console.WriteLine(student2.IsRegisteredForACourse());
}
private static string GetConnectionString()
{
IConfigurationRoot configuration = new ConfigurationBuilder()
.SetBasePath(Directory.GetCurrentDirectory())
.AddJsonFile("appsettings.json")
.Build();
return configuration["ConnectionString"];
}
}
}
Console Output
False
True
True
When you declare a mapped property in an EF entity as virtual, EF generates a proxy which is capable of intercepting requests and assessing whether the data needs to be loaded. If you attempt to use a backing field before that virtual property is accessed, EF has no "signal" to lazy load the property.
As a general rule with entities you should always use the properties and avoid using/accessing backing fields. Auto-initialization can help:
public virtual IReadOnlyList<Course> Courses => new List<Course>().AsReadOnly();
I try to use EF core, but only a part of my model is saved to the database.
This is my model:
public class EngineType
{
public string Name { get; set; }
}
public class Car
{
public long CarId { get; set; }
public string Name { get; set; }
public EngineType Engine { get; set; }
}
The CarId and the Name is saved, but not the EngineType.
This is the test I use, but actual.Engine is always null:
[TestMethod]
public void WhenIAddAndSaveANewCarThenItIsAddedToDB()
{
using var target = new EFCoreExampleContext();
using var concurrentContext = new EFCoreExampleContext();
var expected = new Car() {CarId = 0815, Name = "Isetta", Engine = new EngineType() { Name = "2Takt" }};
target.Cars.Add(expected);
target.SaveChanges();
var actual = concurrentContext.Cars.Single();
Assert.AreEqual(1, concurrentContext.Cars.Count());
Assert.IsNotNull(actual.Engine);
Assert.AreEqual(expected, actual);
}
My Context looks like this:
public class EFCoreExampleContext : DbContext
{
public DbSet<Car> Cars { get; set; }
protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
{
optionsBuilder.UseInMemoryDatabase(databaseName: "Add_writes_to_database");
}
protected override void OnModelCreating(ModelBuilder modelBuilder)
{
modelBuilder.Entity<EngineType>(
d =>
{
d.HasKey(e => e.Name);
d.Property(e => e.Name).IsRequired();
});
modelBuilder.Entity<EngineType>(
d =>
{
d.HasKey(e => e.Name);
});
modelBuilder.Entity<Car>(
d =>
{
d.HasKey(e => e.CarId);
d.Property<DateTime>("LastChanged").IsRowVersion().ValueGeneratedOnAddOrUpdate();
d.Property<string>("EngineForeignKey");
d.HasOne(e => e.Engine)
.WithMany()
.HasForeignKey("EngineForeignKey")
.IsRequired();
});
}
}
Any idea what am I doing wrong (or which existing topic answers this question - I even didn't have the right search words to find it).
Thanks!
I think there is no issue with saving. Entity Framework does not do eager loading by default. So you have to explicitly include any navigational properties that should be in result. Try this when you are fetching actual,
using Microsoft.EntityFrameworkCore;
var actual = concurrentContext.Cars.Include(c => c.Engine).Single();
I have an EF6 setup against a sql server db with about 60 tables in it.
I have entities for each table. What i'm trying to do is run the same method against a set of these entities that will be known at runtime.
The method is a qa/qc routine that does some data check on particular fields that are assured to be in each table.
I guess what i want to do is make the entity a parameter to the method so i can call it consecutive times.
I would also want to make a set of entities to pass as the parameter.
something like this:
List<string> entList = new List<string>(){"Table1","Table2","Table3"};
foreach (entName in entList)
{
//create an entity with the string name
//call myQAQCMethod with the entity
}
MyQAQCMethod (entity SomeEntity)
{
//run against this entity
doQAQC(SomeEntity);
}
Can this be done? Is it a job for reflection?
EDIT
using (var context = new Context())
{
var results = context.EntityAs.Where(a => a.Prop1 == e.Prop1)
.Where(a => a.Prop2 == e.Prop2)
.Select(a => new
{
APropertyICareAbout = a.Prop1,
AnotherPropertyICareAbout = a.Prop2
}).ToArray();
}
is precisely want i want to do. The thing is I want to avoid typing this loop 60 times. I think i'm looking for a way to "feed" a set of entities to this single method.
Also, thank you very much for helping me. I'm learning a lot.
You need to abstract an interface (entity framework won't even notice):
interface IQaQcable
{
int CommonInt { get; set; }
string CommonString { get; set; }
}
public class EntityA : IQaQcable
{
public int Id { get; set; }
public int CommonInt { get; set; }
public string CommonString { get; set; }
// other properties and relations
}
public class EntityB : IQaQcable
{
public int Id { get; set; }
public int CommonInt { get; set; }
public string CommonString { get; set; }
// other properties and relations
}
// in some unknown utility class
void MyQaQcMethod<T>(T entity) where T : IQaQcable
{
doSomethingWithIQaQcableProperties(entity.CommonInt, entity.CommonString);
}
// in some unknown test class
void Test()
{
var entities = new List<IQaQcable> { new EntityA(), new EntityB() };
foreach (var e in entities)
MyQaQcMethod(e);
}
Now, you could extract a base class from which each derives that actually implements the CommonInt and CommonString properties for each entity needing them, but that can get kind of tricky with Table-Per-Type/Table-Per-Hierarchy, so I'd start with this, and then consider introducing either an abstract or concrete base class as an improvement.
EDIT
Maybe your looking for something simpler than I first thought, based on your last comment.
Let's give ourselves what the DbContext for this might look like:
class Context : DbContext
{
public virtual DbSet<EntityA> EntityAs { get; set; }
public virtual DbSet<EntityB> EntityBs { get; set; }
}
So, it could just be that you wish to do this:
using (var context = new Context())
{
var results = context.EntityAs.Where(a => a.Prop1 == e.Prop1)
.Where(a => a.Prop2 == e.Prop2)
.Select(a => new
{
APropertyICareAbout = a.Prop1,
AnotherPropertyICareAbout = a.Prop2
}).ToArray();
}
Keeping in mind, if there is some set of properties in common across entity classes, you could still do something like the following:
IEnumerable<T> MyQaQcMethod(IQueryable<T> entities, T referenceEntity) where T : IQaQcAble
{
return entities.Where(e => SomePredicate(e, referenceEntity));
}
void Test()
{
using (var context = new Context())
{
// EntityA implements IQaQcAble
var resultsForA = MyQaQcMethod(context.EntityAs, defaultEntity).ToArray();
// so does EntityB, so can call with either
var resultsForB = MyQaQcMethod(context.EntityBs, defaultEntity).ToArray();
}
}
Keep in mind, to avoid modifying the generated entity classes, you could implement the interface members — and the interface — in a separate source file using partial classes. E.g.
// IQaQcAble.cs
internal interface IQaQcAble
{
int CommonInt { get; set; }
string CommonString { get; set; }
}
// a class whose existing property names match the interface
public partial class EntityA : IQaQcAble
{
int IQaQcAble.CommonInt
{
get { return CommonInt; }
set { CommonInt = value; }
}
string IQaQcAble.CommonString
{
get { return CommonString; }
set { CommonString = value; }
}
}
// a class whose property names differ
public partial class EntityB : IQaQcAble
{
int IQaQcAble.CommonInt
{
get { return SomeOtherInt; }
set { SomeOtherInt = value; }
}
string IQaQcAble.CommonString
{
get { return SomeOtherInt.ToString(); }
set { SomeOtherInt = Convert.ToInt32(value); }
}
}
I am trying to get the value of a "NotMapped" property for a Entity/class when intercepting a DbUpdateCommandTree.
I have looked through the various metadata, but I cannot find the "link" to the Entity from the CommandTree, so unfortunately I am stuck.
Is it even possible ?
public class SomeEntity
{
public int ID { get; set; }
[NotMapped]
public int SomeUnmappedProperty { get; set; }
}
public class CommandTreeInterceptor : IDbCommandTreeInterceptor
{
public void TreeCreated(DbCommandTreeInterceptionContext ctx)
{
if (ctx.OriginalResult.DataSpace == DataSpace.SSpace)
{
var updateCommand = ctx.OriginalResult as DbUpdateCommandTree;
if (updateCommand != null)
{
// I would like to get a value of a specific property here.
// Pseudo code
var val = updateCommand.Entity.GetPropertyValue("SomeUnmappedProperty") as int;
}
}
}
}
class DemoUser
{
[TitleCase]
public string FirstName { get; set; }
[TitleCase]
public string LastName { get; set; }
[UpperCase]
public string Salutation { get; set; }
[LowerCase]
public string Email { get; set; }
}
Suppose i have demo-class as written above, i want to create some custom annotations like LowerCase,UpperCase etc so that its value gets converted automatically. Doing this will enable me to use these annotations in other classes too.
As Ladislav implied, this is two questions in one.
Assuming you follow the recipe for creating attributes in Jefim's link, and assuming you're calling those created attribute classes "UpperCaseAttribute", "LowerCaseAttribute", and "TitleCaseAttribute", the following SaveChanges() override should work in EF 4.3 (the current version as of the time of this answer post).
public override int SaveChanges()
{
IEnumerable<DbEntityEntry> changedEntities = ChangeTracker.Entries().Where(e => e.State == System.Data.EntityState.Added || e.State == System.Data.EntityState.Modified);
TextInfo textInfo = Thread.CurrentThread.CurrentCulture.TextInfo;
changedEntities.ToList().ForEach(entry =>
{
var properties = from attributedProperty in entry.Entity.GetType().GetProperties()
where attributedProperty.PropertyType == typeof (string)
select new { entry, attributedProperty,
attributes = attributedProperty.GetCustomAttributes(true)
.Where(attribute => attribute is UpperCaseAttribute || attribute is LowerCaseAttribute || attribute is TitleCaseAttribute)
};
properties = properties.Where(p => p.attributes.Count() > 1);
properties.ToList().ForEach(p =>
{
p.attributes.ToList().ForEach(att =>
{
if (att is UpperCaseAttribute)
{
p.entry.CurrentValues[p.attributedProperty.Name] = textInfo.ToUpper(((string)p.entry.CurrentValues[p.attributedProperty.Name]));
}
if (att is LowerCaseAttribute)
{
p.entry.CurrentValues[p.attributedProperty.Name] = textInfo.ToLower(((string)p.entry.CurrentValues[p.attributedProperty.Name]));
}
if (att is TitleCaseAttribute)
{
p.entry.CurrentValues[p.attributedProperty.Name] = textInfo.ToTitleCase(((string)p.entry.CurrentValues[p.attributedProperty.Name]));
}
});
});
});
return base.SaveChanges();
}
You can override the SaveChanges method in your EF context (if you use default code-generation just write a partial class). Something like the following:
public partial class MyEntityContext
{
public override int SaveChanges(SaveOptions options)
{
IEnumerable<ObjectStateEntry> changedEntities =
this.ObjectStateManager.GetObjectStateEntries(
System.Data.EntityState.Added | System.Data.EntityState.Modified);
// here you can loop over your added/changed entities and
// process the custom attributes that you have
return base.SaveChanges(options);
}
}