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C# - how to delete row in realm - android xamarin

i tried this method that I created but it prompts me an error:
Realms.RealmInvalidObjectException:This object is detached. Was it deleted from the realm?'
public void deleteFromDatabase(List<CashDenomination> denom_list)
{
using (var transaction = Realm.GetInstance(config).BeginWrite())
{
Realm.GetInstance(config).Remove(denom_list[0]);
transaction.Commit();
}
}
what is the proper coding for deleting records from database in realm in C# type of coding?

You are doing it the right way. The error message you are getting indicates that the object was removed already. Are you sure it still exists in the realm?
UPDATE:
I decided to update this answer because my comment on the other answer was a bit hard to read.
Your original code should work fine. However, if you want deleteFromDatabase to accept lists with CashDenomination instances that either have been removed already or perhaps were never added to the realm, you would need to add a check. Furthermore, note that you should hold on to your Realm instance and use it in the transaction you created. In most cases, you want to keep it around even longer, though there is little overhead to obtaining it via GetInstance.
public void deleteFromDatabase(List<CashDenomination> denom_list)
{
if (!denom_list[0].IsValid) // If this object is not in the realm, do nothing.
return;
var realm = Realm.GetInstance(config);
using (var transaction = realm.BeginWrite())
{
realm.Remove(denom_list[0]);
transaction.Commit();
}
}
Now, if you want to use identifiers, you could look it up like you do, but still just use Remove:
public void deleteFromDatabase(int denom_id)
{
var realm = Realm.GetInstance(config);
var denom = realm.All<CashDenomination>().FirstOrDefault(c => c.denom_id == denom_id);
if (denom == null) // If no entry with this id exists, do nothing.
return;
using (var transaction = realm.BeginWrite())
{
realm.Remove(denom);
transaction.Commit();
}
}
Finally, if your CashDenomination has denom_id marked as PrimaryKey, you could look it up like this:
public void deleteFromDatabase(int denom_id)
{
var realm = Realm.GetInstance(config);
var denom = realm.ObjectForPrimaryKey<CashDenomination>(denom_id);
if (denom == null) // If no entry with this id exists, do nothing.
return;
using (var transaction = realm.BeginWrite())
{
realm.Remove(denom);
transaction.Commit();
}
}

public void deleteFromDatabase(Realm realm, long cashDenominatorId)
{
realm.Write(() =>
{
var cashDenominator = realm.All<Person>().Where(c => c.Id == cashDenominatorId);
Realm.RemoveRange<CashDenomination>(((RealmResults<CashDenomination>)cashDenominator));
});
}
Which you would call as
Realm realm = Realm.GetInstance(config);
var denom_list = ...
// ...
deleteFromDatabase(realm, denom_list[0].id);

I already made it having this code :) thanks to #EpicPandaForce 's answer.
public void deleteFromDatabase(int denom_ID, int form_ID)
{
//Realm realm;
//and
//RealmConfiguration config = new RealmConfiguration(dbPath, true);
//was initialized at the top of my class
realm = Realm.GetInstance(config);
realm.Write(() =>
{
var cashflow_denom = realm.All<CashDenomination>().Where(c => c.denom_id == denom_ID);
var cashflow_form = realm.All<CashForm>().Where(c => c.form_id == form_ID);
realm.RemoveRange(((RealmResults<CashDenomination>)cashflow_denom));
realm.RemoveRange(((RealmResults<CashForm>)cashflow_form));
});
}
it is now deleting my data without exception :)

Updating Entity in EF6 gives primary key exception

When I try to update this object in EF6 I get an error stating more than 1 entity has this primary key. Looking at this DB I know this to be untrue(from what I can see).
I need to be able to update a second object based on one of the properties on the posted object. The code below produces the error. I have left in commented out pieces that I have tried to get this to work.
public async Task<ActionResult> Edit(PricingRule pricingRule)
{
if(ModelState.IsValid)
{
var currentUser = await serv.UserManager.FindByIdAsync(User.Identity.GetUserId());
var company = currentUser.Company;
//var entityRule = serv.PricingService.PricingRules.Get(pricingRule.PricingRuleId);
//If this is the first rule, set it to the company default
var rulesCount = company.PricingRules.Count;
if (rulesCount <= 1 || company.DefaultPricingRule == null)
pricingRule.DefaultPricingRule = true;
//Make sure no other rules are marked as default, and update the company with this rule as default
if (pricingRule.DefaultPricingRule)
{
if (company.DefaultPricingRule != null)
{
var oldRule = serv.PricingService.PricingRules.Get(company.DefaultPricingRule.PricingRuleId);
oldRule.DefaultPricingRule = false;
//serv.PricingService.PricingRules.Update(oldRule);
}
company.DefaultPricingRule = pricingRule;
serv.CoreService.Companies.Update(company);
}
serv.PricingService.PricingRules.Update(pricingRule);
await serv.SaveAllChangesAsync();
return RedirectToAction("Index");
}
return View(pricingRule);
}

Whether or not it is the best practice or how it should technically be done, this is how I solved my problem.
The edited object I was passing in, needed to be marked as modified first, before doing any other operations. I am assuming this is because the context could then grab it and all other operations regarding it would be done "within context". Other wise I think it was trying to add a new object if I tried to attach it to company.DefaultPricingRule.
public async Task<ActionResult> Edit(PricingRule pricingRule)
{
if(ModelState.IsValid)
{
serv.PricingService.PricingRules.Update(pricingRule);
var currentUser = await serv.UserManager.FindByIdAsync(User.Identity.GetUserId());
var company = currentUser.Company;
//If this is the first rule, set it to the company default
var rulesCount = company.PricingRules.Count;
if (rulesCount <= 1 || company.DefaultPricingRule == null)
pricingRule.DefaultPricingRule = true;
//Make sure no other rules are marked as default, and update the company with this rule as default
if (pricingRule.DefaultPricingRule)
{
if (company.DefaultPricingRule != null)
{
var oldRule = serv.PricingService.PricingRules.Get(company.DefaultPricingRule.PricingRuleId);
oldRule.DefaultPricingRule = false;
serv.PricingService.PricingRules.Update(oldRule);
}
company.DefaultPricingRule = pricingRule;
serv.CoreService.Companies.Update(company);
}
await serv.SaveAllChangesAsync();
return RedirectToAction("Index");
}
return View(pricingRule);
}
If Anyone has a comment on if this is best practice or if there is a better way to do it, I gladly take criticism.

"The operation cannot be completed because the DbContext has been disposed"

I am new at Entity Framework Code first and I am building a small app to get used to it.When the site runs for the first time I access existing catalog values inside the database and display this in a drop down using razor.
public void GetCats()
{
using (context = new RecipeContext())
{
try
{
var query = (from r in context.Catalogues
select r).Distinct().ToList();
catalogues = query.Select(t => t.CatalogueName.ToString()).ToList();
catalogues.Sort();
}
catch (Exception exe)
{
labMessage = exe.Message;
}
}
}
Now when I try to add Catalogue values to the context I get the above error.
public void AddCatalogue(string catalogueName)
{
using(context = new RecipeContext())
{
try
{
catalogueName = catalogueName.ToLower();
var catalogue = new RecipeCatalogue { CatalogueName = catalogueName };
if (context.Catalogues.Where(t => t.CatalogueName == catalogueName).Count() > 0)
{
labMessage = "The value already exists";
CatalogueNameAdded = false;
return;
}
context.Catalogues.Add(catalogue);
context.SaveChanges();
catalogueNameAdded = true;
labMessage = "a new catalogue record was added";
}
catch (Exception exe)
{
catalogueNameAdded = false;
labMessage = exe.Message;
}
}
}
The values are being added to the database however but still get the above exception.
Advice perhaps as to why I get this error. This is my Controller method which calls the above method.
[HttpPost]
public JsonResult AddNewCatalogue(string catalogueName)
{
ViewModel model = new ViewModel();
model.AddCatalogue(catalogueName);
return Json(new { ViewModel = model });
}

Is context a field in your model?
I think you shouldn't assign to a field in a using statement. At the closing brace of the using context will be disposed. If you access that field in another place (without re-assigning) you are accessing a disposed object that might raise the exception you are getting.
Try changing your using statetments like this using (var context = new RecipeContext()).
(note var before context) and drop the field.

Your context is being disposed when the using block where you're performing your query is exited. That's the whole point of the using statement:
using(context = new RecipeContext()) {
// ...
}
// context has been disposed at this point
Instead of a using statement, give your class a field to hold a reference to it.
private RecipeContext _context;
public void GetCats() {
_context = new RecipeContext();
// ...
}
public void AddCatalogue(string catalogueName) {
// Use _context here
}
Just make sure that at some point, you call _context.Dispose(). Also, it's probably better to create the context in the constructor or someplace else that's only called once, prior to performing any operations with it.

Just my 2 cents:
The above answers are correct! If you're using some pattern like a repository, I sugest to implement it as a singleton! This way your objects will not be detached, and you're context will not be disposed!

Enity Framework updating with a child table causing errors

I have the following update function
public void UpdateBatchDefinition(BatchDefinition batchToUpdate)
{
if (batchToUpdate == null)
{
throw new ArgumentNullException("batchToUpdate");
}
BatchDefinition foundDefinition =
this.context.BatchDefinitions.SingleOrDefault(definition => definition.Id == batchToUpdate.Id);
if (foundDefinition != null)
{
if (!string.IsNullOrWhiteSpace(batchToUpdate.Name))
{
foundDefinition.Name = batchToUpdate.Name;
}
if (!string.IsNullOrWhiteSpace(batchToUpdate.Description))
{
foundDefinition.Description = batchToUpdate.Description;
}
if (!string.IsNullOrWhiteSpace(batchToUpdate.LoadType))
{
foundDefinition.LoadType = batchToUpdate.LoadType;
}
if (batchToUpdate.JobId != Guid.Empty)
{
foundDefinition.JobId = batchToUpdate.JobId;
}
foundDefinition.Tables = batchToUpdate.Tables;
this.context.SaveChanges();
}
}
the issue I am having Is when I am trying to update the Tables list. Tables is a List of Table and Table is a Entity of another table
Tables could be added to, removed from or left alone. I need to update that with what ever is being passed in
when I run this right now I get an 'EntityValidationErrors' error, though it wont tell me what the validation issue actually is.
on Inserting I got the same error but was able to fix it using the following
var underlyingContext = this.context as DbContext;
if (underlyingContext != null)
{
foreach (var table in batchDefinition.Tables)
{
// Need to mark the table entity as unchanged or
// else EF will treat it as a new table
underlyingContext.Entry(table).State = EntityState.Unchanged;
}
}
so I tried using that in this update function
var underlyingContext = this.context as DbContext;
if (underlyingContext != null)
{
foreach (var table in foundDefinition.Tables)
{
// Need to mark the table entity as unchanged or
//else EF will treat it as a new table
underlyingContext.Entry(table).State = EntityState.Unchanged;
}
}
foundDefinition.Tables = batchToUpdate.Tables;
and I get the following error instead:
AcceptChanges cannot continue because the object's key values conflict
with another object in the ObjectStateManager. Make sure that the key
values are unique before calling AcceptChanges.
Any thoughts one what I am missing here?

Change end of your update method like this:
foreach (var t in foundDefinition.Tables.ToList())
Context.Tables.Remove(t);
foundDefinition.Tables = batchToUpdate.Tables;
this.context.SaveChanges();
And about your last error, it is said that there are some duplicates in your context. So, EF can't save the context changes into the db (because there are duplicates in the context!)
In fact, I don't know the last error is from add or delete - you didn't mention clearly. So, I don't know the last two code samples are from your add method, or your update method...
However for update, the trick I mentioned here, must solve your problem for update...

Checking individual fields for changes in an EntityState

In our database we have a user. A user can have certain metadata (Like their location, age, etc) associated with them. In addition to that they have a profile image.
A user can edit any of these things at any time.
The problem we run into is that when a user goes to edit their information, but they don't choose an image -- the previous image gets erased (Null).
I figure that when we go to save the modified user, we should be able to say if(user.profileImage == null) don't save it
I figure that would come into play in our user repository which uses the following code:
public void SaveUser(Domain.Entities.User user)
{
if (user.UserId == 0)
{
context.Users.Add(user);
}
else
{
context.Entry(user).State = EntityState.Modified;
//The logic would be here
}
context.SaveChanges();
}
However I seems that no matter what we try it doesn't work.
So my question is: Is there a way to check changes to individual fields instead of the entire EntityState?

I ended up storing image data in the Session and then if the image upload was null I simply inserted the session attribute into my image, effectively keeping the old image if left empty.
Session["image"] = productService.GetProduct(id).Image;
Then in the post I said...
if (image != null)
{
product.ImageType = image.ContentType;
product.Image = new byte[image.ContentLength];
image.InputStream.Read(product.Image, 0, image.ContentLength);
}
else
{
product.Image = (byte[])Session["image"];
}

Yes, there is a way:
context.Users.Attach(user);
context.Entry(user).Property(u => u.Location).IsModified = true;
context.Entry(user).Property(u => u.Age).IsModified = true;
// etc.
Be aware that you cannot set IsModified to false once the property is marked as modified. So, something like this ...
context.Entry(user).State = EntityState.Modified;
context.Entry(user).Property(u => u.Image).IsModified = false;
... does not work.
Edit Alternative solution:
public void SaveUser(Domain.Entities.User user)
{
if (user.UserId == 0)
{
context.Users.Add(user);
}
else
{
var userInDb = context.Users.Single(u => u.UserId == user.UserId);
if (user.profileImage == null)
user.profileImage = userInDb.profileImage;
context.Entry(userInDb).CurrentValues.SetValues(user);
}
context.SaveChanges();
}
This keeps the value of profileImage as it is in the database if the user didn't post a new image (= user.profileImage == null), otherwise it saves the new image.