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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.

Add or Update a Record?

I have an MVC application with the following code in the POST method of the controller. I am doing an EF Add and obviously that is not right. I want it to add the record if it doesn't exist, otherwise Update. How can I do that please?
try
{
AttributeEntities db = new AttributeEntities();
IEnumerable<string> items = viewModel.SelectedAttributes2;
int i = 0;
foreach (var item in items)
{
var temp = item;
// Save it
SelectedHarmonyAttribute attribute = new SelectedHarmonyAttribute();
attribute.CustomLabel = viewModel.ItemCaptionText;
attribute.IsVisible = viewModel.Isselected;
string harmonyAttributeID = item.Substring(1, 1);
// attribute.OrderNumber = Convert.ToInt32(order);
attribute.OrderNumber = i++;
attribute.HarmonyAttribute_ID = Convert.ToInt32(harmonyAttributeID);
db.SelectedHarmonyAttributes.Add(attribute);
db.SaveChanges();
}
}

You would need to check the database for the record you are trying to add/update. If the look-up returns null, that means that it doesn't exist in the database. If it does, you can modify the record that you looked up and call db.SaveChanges() to persist the changes you made to the database.
Edit:
int id = Convert.ToInt32(harmonyAttributeID);
var existingEntry = db.SelectedHarmonyAttributes.SingleOrDefault(x => x.HarmonyAttribute_ID == id);

One common way to determine an add or update is by simply looking at an identifier field, and setting the appropriate state.
using System.Data;
SelectedHarmonyAttribute attribute;
using (var db = new YourDbContext())
{
db.Entry(attribute).State = attribute.HarmonyAttribute_ID == 0 ? EntityState.Added : EntityState.Modified;
db.SaveChanges();
}

You could import the System.Data.Entity.Migrations namespace and use the AddOrUpdate extension method:
db.SelectedHarmonyAttributes.AddOrUpdate(attribute);
db.SaveChanges();
EDIT:
I'm assuming that SelectedHarmonyAttributes is of type DbSet
EDIT2:
Only drawback with doing it this way (and it may not be a concern for you), is that your entity isn't responsible for it's own state change. This means that you can update any property of the entity to something invalid, where you might want to internally validate it on the entity itself or maybe do some other processing you always want to occur on update. If these things are a concern for you, you should add a public Update method onto the entity and check for its existence on the database first. e.g:
var attribute = db.SelectedHarmonyAttributes.SingleOrDefault(x => x.HarmonyAttribute_ID == harmonyAttributeID);
if (attribute != null)
{
attribute.Update(viewModel.ItemCaptionText, viewModel.Isselected, i++);
}
else
{
attribute = new Attribute(viewModel.ItemCaptionText, viewModel.Isselected);
db.SelectedHarmonyAttributes.Add(attribute);
}
db.SaveChanges();
Your update method might look something like:
public void Update(string customLabel, bool isVisible, int orderNumber)
{
if (!MyValidationMethod())
{
throw new MyCustomException();
}
CustomLabel = customLabel;
IsVisible = isVisible;
OrderNumber = orderNumber;
PerformMyAdditionalProcessingThatIAlwaysWantToHappen();
}
Then make all of the entities' properties public "get" but protected "set" so they can't be updated from outside the entity itself. This might be going off an a bit of a tangent but using the AddOrUpdate method would assume you don't want to control the way an update occurs and protect your domain entity from getting into an invalid state etc. Hope this helps!

Error while adding a row and then updating a row using EF

Currently I am attempting to add a new row to a database table through AJAX which is working fine. But then I try to update a different table and I get an error. Here is my code and the error I am encountering.
Error
The object cannot be attached because it is already in the object context. An object can only be reattached when it is in an unchanged state.
Line 41: _db.ChampionCounters.Attach(champion);
Code
[HttpPost]
public ActionResult VoteYes(int id)
{
string results;
if (Request.IsAuthenticated)
{
var checkFirst =
from c in _db.UserCounterLinks
where c.counterId == id && c.userName == User.Identity.Name
select c;
if (checkFirst.Any())
{
results = "You have already voted on this counter.";
return Json(results);
}
var userVoteLink = new UserCounterLink { counterId = id, userName = User.Identity.Name, userAgree = true };
_db.UserCounterLinks.AddObject(userVoteLink);
var champion = _db.ChampionCounters.SingleOrDefault(c => c.id == id);
if (champion != null)
{
champion.positiveVotes++;
_db.ChampionCounters.Attach(champion);
}
_db.SaveChanges();
results = "Voted";
} else
{
results = "You must be logged in to vote.";
}
return Json(results);
}
Summary
The code above is from the controller that handles the Ajax post. Like I said the userVoteLink table creates a record just fine. But when I try to update the other table ChampionCounters the error is thrown.
Thanks in advance!

You don't need to attach the instance because the context is already tracking that instance. Just remove the _db.ChampionCounters.Attach(champion); line.

How to Update with LINQ?

currently, I'm doing an update similar to as follows, because I can't see a better way of doing it. I've tried suggestions that I've read in blogs but none work, such as
http://msdn.microsoft.com/en-us/library/bb425822.aspx
and
http://weblogs.asp.net/scottgu/archive/2007/05/19/using-linq-to-sql-part-1.aspx
Maybe these do work and I'm missing some point. Has anyone else had luck with them?
// please note this isn't the actual code.
// I've modified it to clarify the point I wanted to make
// and also I didn't want to post our code here!
public bool UpdateMyStuff(int myId, List<int> funds)
{
// get MyTypes that correspond to the ID I want to update
IQueryable<MyType> myTypes =
database.MyTypes.Where(xx => xx.MyType_MyId == myId);
// delete them from the database
foreach (db.MyType mt in myTypes)
{
database.MyTypes.DeleteOnSubmit(mt);
}
database.SubmitChanges();
// create a new row for each item I wanted to update, and insert it
foreach (int fund in funds)
{
database.MyType mt = new database.MyType
{
MyType_MyId = myId,
fund_id = fund
};
database.MyTypes.InsertOnSubmit(mt);
}
// try to commit the insert
try
{
database.SubmitChanges();
return true;
}
catch (Exception)
{
return false;
throw;
}
}
Unfortunately, there isn't a database.MyTypes.Update() method so I don't know a better way to do it. Can sombody suggest what I could do? Thanks.
..as a side note, why isn't there an Update() method?

Eh?
public void UpdateCustomer(int CustomerId, string CustomerName)
{
using (MyDataContext dc = new MyDataContext)
{
//retrieve an object from the datacontext.
// datacontext tracks changes to this instance!!!
Customer customer = dc.Customers.First(c => c.ID = CustomerId);
// property assignment is a change to this instance
customer.Name = CustomerName;
//dc knows that customer has changed
// and makes that change in the database
dc.SubmitChanges();
}
}