i'm sorry if this question has already been asked, but i'm in trouble with my method of updating collection in Entity Framework.
Let me explain the situation :
- I have for example one model CUSTOMER with some properties and a collection of ORDERS (for example).
- Let's imagine we have an admin page on wich we can edit all the ORDERS for a customer, and when we submit the form, it will send us back the object CUSTOMERS with updated ORDERS (some added, some updated and some deleted).
For the moment i use something like this in order to compare old collection and new collection and determine which object i need to delete/update/add
var toRemove = new List<ORDERS>();
var toAdd = new List<ORDERS>();
foreach (
var order in
oldList.Where(
order =>
newList.FirstOrDefault(t => t.link_id == order.link_id) == null))
{
toRemove.Add(order);
}
foreach (
var order in
newList.Where(
order =>
oldList.FirstOrDefault(t => t.link_id == order.link_id) == null))
{
toAdd.Add(order);
}
foreach (var ORDERSe in toRemove)
{
bdd.ORDERS.Remove(ORDERSe);
}
foreach (var ORDERSe in toAdd)
{
ORDERSe.pjt_id = project_id;
bdd.ORDERS.Add(ORDERSe);
}
foreach (
var order in
newList.Where(
order =>
oldList.FirstOrDefault(t => t.link_id == order.link_id) != null))
{
var child = oldList.FirstOrDefault(t => t.link_id == order.link_id);
bdd.Entry(child).CurrentValues.SetValues(order);
}
But i'm unconfortable with this, because in my mind, entity framework should be able to do the work for me !
I was hoping something like :
customer.orders = newOrders;
Did i missed anything about entity framework or ?
Because when i do this, it just duplicate my orders.
Thanks in advance for your answer.
You can certainly make it cleaner using .Except() and .Intersect(), but the concept doesn't really change, AFAIK you still have to individually remove, update & add the entries in loops...
var oldList = new List<ORDERS>();
var newList= new List<ORDERS>();
var IdsToRemove = oldList.Select(t => t.link_id).Except(newList.Select(t => t.link_id));
var IdsToAdd = newList.Select(t => t.link_id).Except(oldList.Select(t => t.link_id));
var IdsToUpdate = newList.Select(t => t.link_id).Intersect(oldList.Select(t => t.link_id));
//remove
bdd.orders.where(x => IdsToRemove.Contains(x.link_id)).ForEach(x => bdd.Remove(x));
//add
foreach(var order in newList.Where(x -> IdsToAdd.Contains(x.link_id))
{
bdd.Orders.Attach(order);
bdd.Entries(order).EntityState = EntityState.Added;
}
//update
foreach(var order in newList.Where(x -> IdsToUpdate .Contains(x.link_id))
{
bdd.Orders.Attach(order);
bdd.Entries(order).EntityState = EntityState.Modified;
}
bdd.SaveChanges();
But i'm unconfortable with this, because in my mind, entity framework
should be able to do the work for me !
In fact, EF does the Work for you. Using the data context SaveChanges method EF should be able to save all your changes at once:
DbContext.SaveChanges()
For your convinience you can still override this method. Internally you should use something like this:
public override int SaveChanges()
{
var changeSet = ChangeTracker.Entries<IAuditable>();
if (changeSet != null)
{
foreach (var entry in changeSet.Where(c => c.State != EntityState.Unchanged))
{
entry.Entity.ModifiedDate = DateProvider.GetCurrentDate();
entry.Entity.ModifiedBy = UserName;
}
}
return base.SaveChanges();
}
Related
var fdPositions = dbContext.FdPositions.Where(s => s.LastUpdated > DateTime.UtcNow.AddDays(-1));
foreach (JProperty market in markets)
{
// bunch of logic that is irrelevant here
var fdPosition = fdPositions.Where(s => s.Id == key).FirstOrDefault();
if (fdPosition is not null)
{
fdPosition.OddsDecimal = oddsDecimal;
fdPosition.LastUpdated = DateTime.UtcNow;
}
else
{
// bunch of logic that is irrelevant here
}
}
await dbContext.SaveChangesAsync();
This block of code will make 1 database call on this line
var fdPosition = fdPositions.Where(s => s.Id == key).FirstOrDefault();
for each value in the loop, there will be around 10,000 markets to loop through.
What I thought would happen, and what I would like to happen, is 1 database call is made
var fdPositions = dbContext.FdPositions.Where(s => s.LastUpdated > DateTime.UtcNow.AddDays(-1));
on this line, then in the loop, it is checking against the local table I thought I pulled on the first line, making sure I still properly am updating the DB Object in this section though
if (fdPosition is not null)
{
fdPosition.OddsDecimal = oddsDecimal;
fdPosition.LastUpdated = DateTime.UtcNow;
}
So my data is properly propagated to the DB when I call
await dbContext.SaveChangesAsync();
How can I update my code to accomplish this so I am making 1 DB call to get my data rather than 10,000 DB calls?
Define your fdPositions variable as a Dictionary<int, T>, in your query do a GroupBy() on Id, then call .ToDictionary(). Now you have a materialized dictionary that lets you index by key quickly.
var fdPositions = context.FdPositions.Where(s => s.LastUpdatedAt > DateTime.UtcNow.AddDays(-1))
.GroupBy(x=> x.Id)
.ToDictionary(x=> x.Key, x=> x.First());
//inside foreach loop:
// bunch of logic that is irrelevant here
bool found = fdPositions.TryGetValue(key, out var item);
So I have a search-input and checkboxes that passes the values to the controller when there are inputs. And I want to use these values to get something back from the database. The search-input is a string and it works and intended. Here is the code for the search-input:
public async Task<ViewResult> Index(string searchString, List<int> checkedTypes)
{
var products = from p in _db.Products select p;
ViewData["CurrentFilter"] = searchString;
if (!string.IsNullOrEmpty(searchString))
{
products = products.Where(p => p.Name.ToLower().Contains(searchString));
}
return View(products);
}
However the checkboxes values are stored in a list. So basically I want to do the same as the code above, but with a list. So basically an idea is like this:
if(checkedTypes != null)
{
foreach (var i in checkedTypes)
{
products = products.Where(p => p.TypeId == i));
}
}
If I do it like the code above, I just get the last (i) from the loop. Another solution I did was this:
if(checkedTypes != null)
{
var temp = new List<Product>();
foreach (var i in checkedTypes)
{
temp.AddRange(products.Where(p => p.TypeId == i));
}
products = temp.AsQueryable();
}
But when I did it like that I get this error:
InvalidOperationException: The provider for the source IQueryable doesn't implement IAsyncQueryProvider. Only providers that implement IAsyncQueryProvider can be used for Entity Framework asynchronous operations.
So anyone have a solution that I can use? Or is there a better way to handle checkboxes in the controller?
Assuming you are using EF Core (also the same is true for linq2db) - it supports translating filtering with local collection, i.e. Where(x => checkedTypes.Contains(x.SomeId)).
If you have "and" logic to filter by searchString and checkedTypes than you can conditionally add Where clause:
if (!string.IsNullOrEmpty(searchString))
{
products = products.Where(p => p.Name.ToLower().Contains(searchString));
}
if(checkedTypes != null)
{
products = products.Where(p => checkedTypes.Contains(p.TypeId));
}
P.S.
Also you should be able to change your first line to:
var products = _db.Products.AsQueryable();
I am using Entity Framework 5. I would like to build a query (DbQuery?) then execute it on a DbContext. Is it possible?
Normally, I would perform a query like this:
using (var db = new MyDbContext())
{
var nike = db.Products.Where(p => p.Brand == "Nike").OrderBy(p => p.Name);
foreach (var product in nike)
{
Debug.WriteLine(product.Name);
}
}
But can I construct the query before creating the DbContext, and then attach the query to a DbContext instance when I actually want to retrieve the data ?
public IEnumerable<Products> GetProduct(MyDbContext db){
//query created before-hand
var nike = db.Products.Where(p => p.Brand == "Nike").OrderBy(p => p.Name);
return nike;
}
//and then in your method:
using (var db = new MyDbContext()){
var nike = GetProduct(db); //MyDbContext object attached here.
foreach(var product in nike){
Debug.WriteLine(product.Name);
}
}
Maybe this is what you wanted to do? I am not sure.
A solution would be following:
public Func<bool,Products> Filter()
{
return i => i.Brand == "Nike"
}
public Func<bool,Products> Filter(string brandName)
{
return i => i.Brand == brandName;
}
//usage:
db.Products.Where(Filter());
//or
db.Products.Where(Filter("Nike"));
Currently I cannot test, but it might be that you have to use Expression<Func<bool,Brand>>.
Can someone confirm that?
I am seeking any advice or tips on the following method I have that is using LINQ to find a certain property in a Collection that is null and then go through the results (sub-list) and execute a method on another property from the same Collection.
private void SetRaises()
{
if (employeeCollection != null)
{
var noRaiseList = employeeCollection .Where(emp => emp.Raise == null).ToList();
foreach (var record in noRaiseList )
{
CalculateRaise(record);
}
}
}
public void CalculateRaise(Employee emp)
{
if (emp!= null)
emp.Raise = emp.YearsOfService * 100;
}
The part I don't like in the first method, SetRaises(), is the following snippet:
foreach (var record in noRaiseList )
{
CalculateRaise(record);
}
Is there a way to integrate that part into my LINQ expression directly, i.e. some extension method I am not aware of?
Thank you!
The first thing you could do would be: don't generate an intermediate list:
var pending = employeeCollection.Where(emp => emp.Raise == null);
foreach (var record in pending)
{
CalculateRaise(record);
}
which is identical to:
foreach (var record in employeeCollection.Where(emp => emp.Raise == null))
{
CalculateRaise(record);
}
This is now non-buffered deferred execution.
But frankly, the LINQ here isn't giving you much. You could also just:
foreach(var emp in employeeCollection)
{
if(emp.Raise == null) CalculateRaise(emp);
}
If you don't need list of employees without Raise you can do this in one line:
employeeCollection.Where(emp => emp.Raise == null).ToList().ForEach(x => x.Raise = x.YearsOfService * 100);
You could use the ForEach chain-method. But that's only sugar syntax.
employeeCollection.Where(emp => emp.Raise == null)
.ToList()
.ForEach(record => CalculateRaise(record))
It should be something like this:
var noRaiseList = employeeCollection .Where(emp => emp.Raise == null).ToList().ForEach(e=>e.Raise = e.YearsOfService * 100);
I have a method that updates a ReportRecipient object in EF. The primitives work fine; the headache comes in when trying to manage a M2M relationship with the RecipientGroups objects.
Please take a look at this code:
public IReportRecipient ModifyRecipientWithGroupAssignments(IEnumerable<Guid> groupIds, IReportRecipient recipient)
{
var entity = Context.ReportRecipients
.Include("RecipientGroups")
.FirstOrDefault(e => e.ReportRecipientId == recipient.ReportRecipientId)
.FromIReportRecipient(recipient);
var toRemove = entity.RecipientGroups
.Where(e => !groupIds.Contains(e.GroupId))
.ToList();
//remove group assignments that no longer apply
foreach (var group in toRemove)
{
if (group != null)
{
entity.RecipientGroups.Attach(group);
entity.RecipientGroups.Remove(group);
}
}
var toAdd = entity.RecipientGroups
.Where(e => groupIds.Contains(e.GroupId))
.ToList();
//add new groups that weren't there before
foreach (var group in toAdd)
{
if (group != null)
{
entity.RecipientGroups.Attach(group);
}
}
return entity;
}
... my problem is on the var ToAdd... line. Even if I have a collection of Guids in groupIds that match Guids representing RecipientGroup objects in the database, toAdd always evaluates to an empty collection. I would think the Contains() function would work for this scenario; can someone please explain if I am doing something wrong?
You should load the RecipientGroups you want to add from the database (Context.RecipientGroups I guess), not from the collection you want to add them to (entity.RecipientGroups in the code sample).