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DBSet.Find() API missing in Entity Framework Core Final RC1 Version
Rahul Sahay
Apr 05, 2016
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In this blog you will learn DBSet.Find() API missing in Entity Framework Core Final RC1 Version.
Recently, I was writing the infrastructure part of My Movie Review SPA app using ASP.NET Core version. Then, I landed in a really weird situation where in DBSet.Find() a piece is missing. This is a really crucial extension method for finding the record based on the primary key. In order to find the solution, I thought it would be nice to talk to EF Guru Julie Lerman directly. Here is what I asked her and what she replied on the same.
Here, at this point I got the confirmation, this feature is yet to be included by EF Team. Hence, I decided to use the interim solution provided by the EF Team themselves. Below is the extension method which I have written to serve the same result.
using
System;
using
System.Linq;
using
System.Linq.Expressions;
using
Microsoft.Data.Entity;
using
Microsoft.Data.Entity.Infrastructure;
namespace
MovieReviewSPA.Data.Helpers
{
public
static
class
Extensions
{
public
static
TEntity Find<TEntity>(
this
DbSet<TEntity>
set
,
params
object
[] keyValues) where TEntity :
class
{
var context = ((IInfrastructure<IServiceProvider>)
set
).GetService<DbContext>();
var entityType = context.Model.FindEntityType(
typeof
(TEntity));
var key = entityType.FindPrimaryKey();
var entries = context.ChangeTracker.Entries<TEntity>();
var i = 0;
foreach
(var property
in
key.Properties)
{
entries = Enumerable.Where(entries, e => e.Property(property.Name).CurrentValue == keyValues[i]);
i++;
}
var entry = entries.FirstOrDefault();
if
(entry !=
null
)
{
// Return the local object if it exists.
return
entry.Entity;
}
// TODO: Build the real LINQ Expression
// set.Where(x => x.Id == keyValues[0]);
var parameter = Expression.Parameter(
typeof
(TEntity),
"x"
);
var query = Queryable.Where(
set
, (Expression<Func<TEntity,
bool
>>)
Expression.Lambda(
Expression.Equal(
Expression.Property(parameter,
"Id"
),
Expression.Constant(keyValues[0])),
parameter));
// Look in the database
return
query.FirstOrDefault();
}
}
}
And, here is the completed Repository Pattern for my project.
using
System;
using
System.Linq;
using
Microsoft.Data.Entity;
using
Microsoft.Data.Entity.ChangeTracking;
using
MovieReviewSPA.Data.Contracts;
using
MovieReviewSPA.Data.Helpers;
using
DbContext = Microsoft.Data.Entity.DbContext;
using
EntityState = Microsoft.Data.Entity.EntityState;
namespace
MovieReviewSPA.Data
{
public
class
EFRepository<T> : IRepository<T> where T :
class
{
public
EFRepository(DbContext dbContext)
{
if
(dbContext ==
null
)
throw
new
ArgumentNullException(
"dbContext"
);
DbContext = dbContext;
DbSet = DbContext.Set<T>();
}
protected
DbContext DbContext {
get
;
set
; }
protected
DbSet<T> DbSet {
get
;
set
; }
public
virtual
IQueryable<T> GetAll()
{
return
DbSet;
}
public
virtual
T GetById(
int
id)
{
//EF Core Will be updated shortly with Find Extension by Default
//Here, I have written Extension method for the same
//Source:- http://stackoverflow.com/questions/29030472/dbset-doesnt-have-a-find-method-in-ef7/29082410#29082410
return
DbSet.Find(id);
}
public
virtual
void
Add(T entity)
{
EntityEntry<T> dbEntityEntry = DbContext.Entry(entity);
if
(dbEntityEntry.State != (EntityState) EntityState.Detached)
{
dbEntityEntry.State = EntityState.Added;
}
else
{
DbSet.Add(entity);
}
}
public
virtual
void
Update(T entity)
{
EntityEntry<T> dbEntityEntry = DbContext.Entry(entity);
if
(dbEntityEntry.State != (EntityState) EntityState.Detached)
{
DbSet.Attach(entity);
}
dbEntityEntry.State = EntityState.Modified;
}
public
void
Delete(T entity)
{
EntityEntry<T> dbEntityEntry = DbContext.Entry(entity);
if
(dbEntityEntry.State != (EntityState) EntityState.Deleted)
{
dbEntityEntry.State = EntityState.Deleted;
}
else
{
DbSet.Attach(entity);
DbSet.Remove(entity);
}
}
public
void
Delete(
int
id)
{
var entity = GetById(id);
if
(entity ==
null
)
return
;
Delete(entity);
}
}
}
Now, below is the glimpse of the solution structure so far for my Movie Review SPA coming up using ASP.NET Core, WEB-API, Angular JS, Entity Framework and tons of new things.
I hope you have liked this discussion. Thanks for joining me.
DBSet.Find API missing
Entity Framework Core
Final RC1 Version
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