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WPF and Databases

http://schoolacademy.telerik.com. WPF and Databases. Linq -to-Entities, Data Persisters , Master Datail. Doncho Minkov. Telerik School Academy. http://schoolacademy.telerik.com. Technical Trainer. http://www.minkov.it. Table of Contents. Data Access Layer Linq -to-Entities

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WPF and Databases

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  1. http://schoolacademy.telerik.com WPF and Databases Linq-to-Entities, Data Persisters, Master Datail Doncho Minkov Telerik School Academy http://schoolacademy.telerik.com Technical Trainer http://www.minkov.it

  2. 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

  3. Data Access Layer

  4. Data Access Layer • The Data Access Layer is a essential • Used for access to the database • Class Library with single EntityModelclass • This way we can use the same DAL with many applications

  5. Data Access Layer Live Demo

  6. Accessing the Data Layer

  7. 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>

  8. Accessing DAL • After instantiating the EntityModelwe 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 DataPersisterobject <TreeView x:Name="TreeViewCategories" ItemsSource="{Binding Categories}">

  9. Accessing the Data Layer Live Demo

  10. Master Detail

  11. 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"/> <ListViewDisplayMemberPath="Name" ItemsSource="{Binding ElementName=ListViewFamilies, Path=SelectedItem}"/>

  12. Master Datail in MVVM • Consider we have the property Categories in the ViewModel • Somehow it gets data from the Model • Since Categories is a IEnumerablewe can get its ICollectionView • Now we got the CurrentItem • Can make property Products that returns the products of the CurrentItem

  13. Master Detail Live Demo

  14. Data Persister The way to collect information

  15. 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

  16. 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

  17. Data Persister Live Demo

  18. Paging What is paging and why we need it?

  19. 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?

  20. Paging • TODO

  21. Paging Live Demo

  22. WPF and Databases With MVVM

  23. 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>

  24. Categories Editor Live Demo

  25. WPF and Databases

  26. Exercises • 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. • Implement add / edit / delete for the continents, countries, towns and languages. Handle the possible errors accordingly.Implement validation logic.

  27. Exercises (2) • 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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