WPF and DatabasesLinq-to-Entities, Data Persisters, Master Datail
Doncho Minkov
Telerik School Academyhttp://schoolacademy.telerik.com
Technical Trainerhttp://www.minkov.it
http://schoolacademy.telerik.com
Table of Contents Data Access Layer
Linq-to-Entities Linq-to-XML
Accessing the Data Layer DataContext
Master Detail Data Persister Paging WPF and Databases
Data Access Layer
Data Access Layer The Data Access Layer is a essential Used for access to the database
Class Library with single EntityModel class
This way we can use the same DAL with many applications
Data Access LayerLive Demo
Accessing the Data Layer
The DataContext When adding a reference to the DAL
project We can instantiate an entity model
in the XAML And set it for DataContext<Window … xmlns:datalayer=" clr-namespace:NorthwindDataLayer;assembly= NorthwindDataLayer"> <Window.DataContext> <datalayer:NorthwindEntities /> </Window.DataContext>
Accessing DAL After instantiating the EntityModel
we can simply bind some of the entities to a ItemCollection ListBox, ListView, TreeView, etc.
In MVVM it is not possible to access the DAL directly Done through the ViewModel In MVVM we need a DataPersister
object
<TreeView x:Name="TreeViewCategories" ItemsSource="{Binding Categories}">
Accessing the Data LayerLive Demo
Master Detail
Master Detail What is Master Detail?
When selecting a Category Show category info Show products in this category
<ListView Name="ListViewFamilies" ItemsSource="{Binding}" DisplayMemberPath="FamilyName"/><ListView DisplayMemberPath="Name" ItemsSource="{Binding ElementName=ListViewFamilies, Path=SelectedItem}"/>
Master Datail in MVVM Consider we have the property Categories in the ViewModel Somehow it gets data from the
Model Since Categories is a IEnumerable
we can get its ICollectionView Now we got the CurrentItem Can make property Products that
returns the products of the CurrentItem
Master DetailLive Demo
Data PersisterThe way to collect information
What is a Data Persister?
The Data Persister is the object that gives data to the Model Sometimes it is merged with the
Model It could be an EntityDataModel It could be a Linq-to-XML object It could just an object we created
How the Data Persister helps? Easier for mocking (unit testing) Better reusability
The DataPersister The DataPersister is the class that makes the connection with the Data (RDB, XML or object) Responsible for the CRUD May have validation
With this object the Model is pretty clean Almost no programming logic Loose coupling
Data PersisterLive Demo
PagingWhat is paging and why we need it?
What is Paging? A memory-management scheme
A computer can store and retrieve data from secondary storage for use in main memory
With paging the application retrieves data from secondary storage in same-size blocks called pages
Why use paging? Imagine a Database with over a
million records Store them in the dynamic memory
at once? Or take them by pieces with 100
records?
Paging TODO
PagingLive Demo
WPF and DatabasesWith MVVM
WPF and Databases Consider the usual case
You have categories with products in a Database
CRUD operations should be implemented
You have the following:
When selecting the DataContext of the Grid You get a Person object
<Grid DataContext="{Binding Person}"> <TextBox Text="{Binding Name}"/> <TextBox Text="{Binding Age}"/></Grid>
Categories EditorLive Demo
Questions?
WPF and Databases
Exercises1. Create a database holding continents,
countries and town. Countries have name, language, population and continent. Towns have name, population and country. Implement a WPF application that shows the continents in a ComboBox, countries in a ListView and the towns in a ListView and allows master-detail navigation. Use Entity Framework. Use paging and sorting for the long lists.
2. Implement add / edit / delete for the continents, countries, towns and languages. Handle the possible errors accordingly. Implement validation logic.
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Exercises (2)3. Add a flag for each country which
should be a PNG image, stored in the database, displayed along with the country data. Implement "change flag" functionality by uploading a PNG image.
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