Meskipun C dibuat untuk memprogram sistem dan jaringan komputer namun bahasa ini juga sering digunakan dalam mengembangkan software aplikasi. C juga banyak dipakai oleh berbagai jenis platform sistem operasi dan arsitektur komputer, bahkan terdapat beberepa compiler yang sangat populer telah tersedia.
C adalah huruf ketiga dalam alfabet Latin. Dalam bahasa Indonesia, huruf ini disebut ce (dibaca [tʃe]).
You can use Include()
first, then retrieve a single object from the resulting query:
Item item = db.Items
.Include(i => i.Category)
.Include(i => i.Brand)
.FirstOrDefault(x => x.ItemId == id);
Dennis' answer is using Include
and SingleOrDefault
. The latter goes round-tripping to database.
An alternative, is to use Find
, in combination with Load
, for explicit loading of related entities...
Below an MSDN example:
using (var context = new BloggingContext())
{
var post = context.Posts.Find(2);
// Load the blog related to a given post
context.Entry(post).Reference(p => p.Blog).Load();
// Load the blog related to a given post using a string
context.Entry(post).Reference("Blog").Load();
var blog = context.Blogs.Find(1);
// Load the posts related to a given blog
context.Entry(blog).Collection(p => p.Posts).Load();
// Load the posts related to a given blog
// using a string to specify the relationship
context.Entry(blog).Collection("Posts").Load();
}
Of course, Find
returns immediately without making a request to the store, if that entity is already loaded by the context.
There's no real easy way to filter with a find. But I've come up with a close way to replicate the functionality but please take note of a few things for my solution.
This Solutions allows you to filter generically without knowning the primary key in .net-core
Find is fundamentally different because it obtains the the entity if it's present in the tracking before Querying the database.
Additionally It can filter by an Object so the user does not have to know the primary key.
This solution is for EntityFramework Core.
Here are some extension methods to add which will help you filter by primary key so
public static IReadOnlyList<IProperty> GetPrimaryKeyProperties<T>(this DbContext dbContext)
{
return dbContext.Model.FindEntityType(typeof(T)).FindPrimaryKey().Properties;
}
//TODO Precompile expression so this doesn't happen everytime
public static Expression<Func<T, bool>> FilterByPrimaryKeyPredicate<T>(this DbContext dbContext, object[] id)
{
var keyProperties = dbContext.GetPrimaryKeyProperties<T>();
var parameter = Expression.Parameter(typeof(T), "e");
var body = keyProperties
// e => e.PK[i] == id[i]
.Select((p, i) => Expression.Equal(
Expression.Property(parameter, p.Name),
Expression.Convert(
Expression.PropertyOrField(Expression.Constant(new { id = id[i] }), "id"),
p.ClrType)))
.Aggregate(Expression.AndAlso);
return Expression.Lambda<Func<T, bool>>(body, parameter);
}
public static Expression<Func<T, object[]>> GetPrimaryKeyExpression<T>(this DbContext context)
{
var keyProperties = context.GetPrimaryKeyProperties<T>();
var parameter = Expression.Parameter(typeof(T), "e");
var keyPropertyAccessExpression = keyProperties.Select((p, i) => Expression.Convert(Expression.Property(parameter, p.Name), typeof(object))).ToArray();
var selectPrimaryKeyExpressionBody = Expression.NewArrayInit(typeof(object), keyPropertyAccessExpression);
return Expression.Lambda<Func<T, object[]>>(selectPrimaryKeyExpressionBody, parameter);
}
public static IQueryable<TEntity> FilterByPrimaryKey<TEntity>(this DbSet<TEntity> dbSet, DbContext context, object[] id)
where TEntity : class
{
return FilterByPrimaryKey(dbSet.AsQueryable(), context, id);
}
public static IQueryable<TEntity> FilterByPrimaryKey<TEntity>(this IQueryable<TEntity> queryable, DbContext context, object[] id)
where TEntity : class
{
return queryable.Where(context.FilterByPrimaryKeyPredicate<TEntity>(id));
}
Once you have these extension methods you can filter like so:
query.FilterByPrimaryKey(this._context, id);
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