Pfthb

So, I have a form with a list of categories binded to a DataGridView, and when I double-click on one of the rows, a new form with details of the category is open, and also allow the user to edit or remove the selected category.

Here is the code of both forms:

FrmCategoryList.cs

public partial class FrmCategoryList : Form

 private readonly DbContext dbContext;

 public FrmCategoryList()
 
 InitializeComponent();
 dbContext = new DbContext();
 

 private void FrmCategoryList_Load(object sender, EventArgs e)
 
 FillGrid();
 

 private void txtSearch_TextChanged(object sender, EventArgs e)
 
 FillGrid();
 

 private void dgvCategories_CellDoubleClick(object sender, DataGridViewCellEventArgs e)
 
 var grid = (DataGridView)sender;
 if (e.RowIndex >= 0)
 
 var category = (Category)grid.Rows[e.RowIndex].DataBoundItem;
 var frmCategoryView = new FrmCategoryView(category.Id, dbContext);

 if (frmCategoryView.ShowDialog() == DialogResult.OK)
 FillGrid();
 
 

 private void btnNew_Click(object sender, EventArgs e)
 
 var frmCategoryView = new FrmCategoryView(0, dbContext);

 if (frmCategoryView.ShowDialog() == DialogResult.OK)
 FillGrid();
 

 private void btnClose_Click(object sender, EventArgs e)
 
 Close();
 

 private void FillGrid()
 
 categoryBinding.DataSource = dbContext.Categories.Where(p => p.Description.StartsWith(txtSearch.Text)).ToList();
 

 private void FrmCategoryList_FormClosing(object sender, FormClosingEventArgs e)
 
 dbContext?.Dispose();
 

FrmCategoryView.cs

public partial class FrmCategoryView : Form

 private readonly DbContext dbContext;
 private Category category;

 public FrmCategoryView(int categoryId, DbContext dbContext)
 
 InitializeComponent();
 this.dbContext = dbContext;

 if (categoryId == 0)
 
 category = new Category();
 btnSave.Visible = true;
 
 else
 
 category = dbContexto.Categories.Include(c => c.Products).FirstOrDefault(c => c.Id == categoryId);
 btnUpdate.Visible = true;
 btnDelete.Visible = true;
 
 

 private void FrmCategoryView_Load(object sender, EventArgs e)
 
 txtDescription.DataBindings.Add("Text", category, "Description");
 

 private void btnSave_Click(object sender, EventArgs e)
 
 if (category.Validate(dbContext))
 
 dbContext.Categories.Add(category);
 dbContext.SaveChanges();

 MessageBox.Show("Category added!", "Info", MessageBoxButtons.OK, MessageBoxIcon.Information);
 DialogResult = DialogResult.OK;
 Close();
 
 

 private void btnUpdate_Click(object sender, EventArgs e)
 
 if (category.Validate(dbContext))
 
 dbContext.Categories.Attach(category);
 dbContext.Entry(category).State = EntityState.Modified;
 dbContext.SaveChanges();

 MessageBox.Show("Category updated!", "Info", MessageBoxButtons.OK, MessageBoxIcon.Information);
 DialogResult = DialogResult.OK;
 Close();
 
 

 private void btnDelete_Click(object sender, EventArgs e)
 
 if (MessageBox.Show("¿Are you sure to delete this category?", "Confirmation", MessageBoxButtons.YesNo, MessageBoxIcon.Question) == DialogResult.Yes)
 
 if (category.Products.Count > 0)
 
 MessageBox.Show("You cannot delete a category with dependencies.", "Error", MessageBoxButtons.OK, MessageBoxIcon.Error);
 return;
 

 dbContext.Categories.Remove(category);
 dbContext.SaveChanges();

 MessageBox.Show("Category deleted!.", "Info", MessageBoxButtons.OK, MessageBoxIcon.Information);
 DialogResult = DialogResult.OK;
 Close();
 
 

 private void btnClose_Click(object sender, EventArgs e)
 
 DialogResult = DialogResult.Cancel;
 Close();
 

So, the problem comes when I edit some field of a category, and then close the form without pressing the Update button. The context isn't disposed until the FrmCategoryList is closed, and the category object from FrmCategoryView is binded to the text, so the context is updated but changes are not saved to the database. So, if I open other category and actually update it, the previous change will be saved too when calling SaveChanges() because the context keep track of the changes that the user "discard".

How can I do to solve this? I could re-initialize the context in FrmCategoryView, but then the changes will not be in FrmCategoryList context in case I actually save something, and I don't know how to force EF to check database even for already tracked objects.

Also, maybe there is some way to detach the object from the context, and then re-attach it when Update button is pressed. I tried with AsNoTracking() but an error happens when trying to re-attach on Update: it's duplicated because an instance of that object was created in the list form.

Sorry for my bad english, I hope you understand!

EDIT:

Now I tried to set the Entity State of category to Detached right after getting it using the Id in FrmCategoryView constructor, with:

dbContext.Entry(category).State = EntityState.Detached;

It doesn't work the first time I close the view form: the grid row get updated because the context is updated, even when the category entry is set as Detached. But the next onces, it doesn't happend. It works like it should work. The changes I make to category aren't tracked by the context until I re-attach it and save changes on Update button.

The problem here is you have used ShowDialog. Read the second point in remarks section of below link

https://docs.microsoft.com/en-us/dotnet/api/system.windows.forms.form.close?view=netframework-4.7.2

In this scenario the form is not disposed.

you have displayed the form using ShowDialog. In these cases, you will
need to call Dispose manually to mark all of the form's controls for
garbage collection.

Or as you want Modal dialog, clean up the context by handling closing event, if you do not have problem with other controls living till you close parent form.

I found a solution.

To recap, this are the changes I made to the original code:

• Added AsNoTracking() when filling the grid in FrmCategoryList.


• Detach category from the context after getting it using the id in FrmCategoryView constructor.


• Re-attach category before saving changes on Update and Delete, with Modified and Deleted states respectively.

After some tests, I didn't find any issue. Any suggestions are appreciated.