filipjaruska / library

Library

This library is a school project for managing a fictional library database connection using Entity Framework Core. It includes the AppDbContext class, which is used to interact with the database.

Please note that some of the comments and chapters in this project and .md file are intended for educational purposes and may not provide practical value to the code or the reader. Most notes will be most likely incomplete or unfinished since in most cases they will only contain information that i either want aware of or wanted to remind my self of.

Github

File Structure

• Data

• Components

  • Data Grid Binder
    • List vs Bindinglist

• Forms

AppDbContext

The AppDbContext class is defined in AppDbContext.cs. It extends the DbContext class from Entity Framework Core and includes DbSet properties for each of the tables in the database.

Database Connection

The XML markup in the configuration file sets up the connection string for the database. The AppDbContext class in AppDbContext.cs uses this connection string to connect to the database. Said configuration file would be located in Library/Data/App.config.

<?xml version="1.0" encoding="utf-8" ?>

<configuration>
  <connectionStrings>
    <add
      name="DefaultConnection"
      connectionString="Host=; Database=; Username=; Password="
      providerName="System.Data.SqlClient"
    />
  </connectionStrings>
  <appSettings>
    <add key="GoogleCustomSearchApiKey" value="ApiKey" />
    <add key="GoogleCustomSearchCx" value="SearchCx" />
</appSettings>
</configuration>

Its also possible to instead replace the connection string configuration manager with the connection string it self.

//App.config solution
 string connectionString = ConfigurationManager.ConnectionStrings["DefaultConnection"].ConnectionString;

 //Hardcoded solution
 string connectionString = "Host=; Database=; Username=; Password=";

Database Configuration

Components

DataGridBinder

DataGridBinder

Generic Types (T and TViewModel) T represents the type of entities in database. TViewModel represents the type of view models that used for displaying data in DataGridView.

Function Parameters

• queryFunc is a function that takes an AppDbContext and returns an IQueryable<T>.

  Note: IQueryable<T> is an interface that represents a collection of objects that can be queried in a LINQ fashion.

• whereFunc is a function that takes an entity of type T and returns a boolean, it defaults to a function that always returns true, meaning no filtering is applied.

• selectFunc is a function that takes an entity of type T and converts it to a view model of type TViewModel.

Using AppDbContext creates a new instance of the AppDbContext class, and the using statement ensures that the context is disposed of correctly when the block is exited.

Note: It's a good practice to wrap database operations in a using statement to ensure proper resource management.

Query Execution

• var query = queryFunc(context); executes the provided queryFunc to get an IQueryable<T> representing the initial set of data from the database.

• var filteredQuery = query.Where(whereFunc ?? (_ => true)); filters the data based on the whereFunc (or a default filter if whereFunc is null).

  Note: The ?? operator is the null-coalescing operator, which means if whereFunc is null, it uses a default filter that always returns true.

• var viewModelList = filteredQuery.Select(selectFunc).ToList();: Projects the filtered entities into view models using the selectFunc and converts the result to a list.

List vs BindingList

A List<> is simply an automatically resizing array, of items of a given type, with a couple of helper functions (eg: sort). It's just the data, and you're likely to use it to run operations on a set of objects in your model.

A BindingList<> is a wrapper around a typed list or a collection, which implements the IBindingList interface. This is one of the standard interfaces that support two-way databinding. It works by implementing the ListChanged event, which is raised when you add, remove, or set items. Bound controls listen to this event in order to know when to refresh their display.

When you set a BindingSource's DataSource to a List<>, it internally creates a BindingList<> to wrap your list. You may want to pre-wrap your list with a BindingList<> yourself if you want to access it outside of the BindingSource, but otherwise it's just the same. You can also inherit from BindingList<> to implement special behavior when changing items.

IEditableObject is handled by the BindingSource. It'll call BeginEdit on any implementing object when you change the data in any bound control. You can then call EndEdit/CancelEdit on the BindingSource and it will pass it along to your object. Moving to a different row will call EndEdit as well.

Fomr orsmghnt

Forms