使用 linq c# 在 datagridview 中显示特定记录

Question

I created a linq with this code:

DataClasses1DataContext DB = new DataClasses1DataContext();

I just want to see a specific record from a view whose first column code is 00080 in the datagirdview1 so that other records are not displayed. What code should I write in the form1_load so I can see it? i get no record in datagridview with this code:

    dataGridView1.DataSource=
        DB.W0_Calc_BedBes_UseInViews.FirstOrDefault(x => x.C_Code =="00080");

Answer 1

A simple linq query would be something like this:

DB.(Tablename).Where(x => x.(Id column name) == 00080)

Answer 2

In modern programming, you separate your model from how your model is displayed (your view). This enables you to change your view without having to change your model, for instance, if you want to show your data as a Graph instead of a table, or if you want to display the data in a Listbox, your model don't have to change.

Similarly, small changes in your model doesn't have to mean that you need to change your view. It will also be possible to unit test your model without needing a windows form

This separation between your model and your view needs adapter code: the ViewModel. Together this is quite often abbreviated as MVVM-model.

Back to your question

Your database contains several tables. Apparently you want to show some data from one of these table in a DataGridView.

The rows in the table are represented by a class. For example:

class Product
{
    public int Id {get; set;}       // primary key
    public string Name {get; set;}
    public string ProductCode {get; set;}
    ...
}

Depending on what kind of method you use to access your database, your DataContext will probably have something like this:

class DataClasses1DataContext : DbContext
{
    public DbSet<Product> Products {get; set;}
    ...
}

Where DbSet<Product> represents your database table with Products. DbSet<Product> implements IQueryable<Product> , so you can use LINQ to fetch specific data from the table with Products.

In your Form you'll need a method like this:

IEnumerable<DisplayedProduct> FetchProductsToDisplay(...)
{
    ... // TODO implement
}

If the Products in the Database are very similar to the Products that you want to Display, you don't need a separate DisplayedProduct class, if not, you need to define this class.

We'll first focus on how to Display fetched records in the DataGridView, later we'll look at how you fetch specific Products, for instance those that have column code 00080.

The View

You decided to display fetched Products in a DataGridView, with several columns. Usually you'll use the designer to add some columns, and to specify the format of the cells in the column. You also have to specify which column should show which property of the DisplayedProduct. For this we use property DataGridViewColumn.DataPropertyName

columnId.DataPropertyName = nameof(DisplayedProperty.Id);
columnName.DataPropertyName = nameof(DisplayedProperty.Name);
columnProductCode.DataPropertyName = nameof(DisplayedProperty.ProductCode);
...

Now to Display the fetched products, all you have to do is assign the data to the DataGridview.DataSource

IEnumerable<DisplayedProduct> productsToDisplay = this.FetchProductsToDisplay(...);
this.dataGridView1.DataSource = productsToDisplay.ToList();

This will be enough to display the fetched products. However, changes that the operator makes, like adding / removing rows, or changing cells, are not reflected in the list.

If you want this, you'll have to put the fetched data into an object that implements IBindingList , like class BindingList .

Simply add a property in your form

private BindingList<DisplayedProduct> DisplayedProducts
{
    get => (BindingList<DisplayedProduct>)this.dataGridView1.DataSource;
    set => this.dataGridView1.DataSource = value;
}

Usage:

private void InitDisplayedProducts()
{
    IEnumerable<DisplayedProduct> productsToDisplay = this.FetchProductsToDisplay(...);
    this.DisplayedProducts = new BindingList<DisplayedProduct>(productsToDisplay.ToList());
}

And presto, your products are displayed. and all changes that the operator makes are automatically recorded, If the operator indicates that he has finished editing the products, for instance by pressing a button: you can process the changes:

private void OnButtonOk_Clicked(object sender, ...)
{
    ICollection<DisplayedProducts> editedProducts = this.DisplayedProducts;
    // check which products are added / removed / changed and process them
    this.ProcessEditedProducts(editedProducts);
}

How to fetch the products that you want to display?

IEnumerable<DisplayedProduct> FetchProductsToDisplay(string productCode)
{
    using (var dbContext = new DataClasses1DataContext())
    {
        // I want only the Products with ProductCode == "00080"
        return dbContext.Products.Where(product => product.ProductCode == productCode)
            .Select(product => new DisplayedProduct
            {
                Id = product.Id,
                Name = product.Name,
                ProductCode = productCode,
                ...
            })
            .ToList();
        }
    }
}

In words: from all Products, keep only those Products that have a value for property ProductCode that equals the input parameter productCode . From every remaining Product, make one new DisplayedProduct object with property values...

If you need to process selected items, consider to add the following to your form:

private DisplayedProduct CurrentProduct = (DisplayedProduct) this.dataGridView1
    .CurrentRow?.DataBoundItem

private IEnumerable<DisplayedProduct> SelectedProducts = this.dataGridView1.SelectedRows
   .Cast<DataGridViewRow>()
   .Select(row => row.DataboundItem)
   .Cast<DisplayedProduct>();

Answer 3

I found it:

dataGridView1.DataSource =
        DB.W0_Calc_BedBes_UseInViews.Where(x => x.C_Code == "00080");