Windows Phone 7.5 - Local SQL Database：总体概况

http://msdn.microsoft.com/en-us/library/hh202860(v=vs.92).aspx

            Windows Phone

 

December 15, 2011

With Windows Phone OS 7.1, you can store relational data in a local database that resides in your application’s isolated storage container. Windows Phone applications use LINQ to SQL for all database operations; LINQ to SQL is used to define the database schema, select data, and save changes to the underlying database file residing in isolated storage. This topic provides an overview of using a local database with your Windows Phone application. For a step-by-step walkthrough of creating an application that uses a local database, see How to: Create a Basic Local Database Application for Windows Phone.

Architectural Overview

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To store and retrieve data in a local database, a Windows Phone application uses LINQ to SQL. LINQ to SQL provides an object-oriented approach to working with data and comprises an object model and a runtime.

The LINQ to SQL object model is made up primarily by the System.Data.Linq.DataContext object, which acts as a proxy for the local database. The LINQ to SQL runtime is responsible for bridging the world of objects (the DataContext object) with the world of data (the local database). This relationship is summarized in the following image.

Data Context

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PhoneNumber columns.

LINQ to SQL Runtime

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LINQ to SQL.

Note:
LINQ to SQL on Windows Phone does not directly support executing Transact-SQL, including Data Definition Language (DDL) or Data Modeling Language (DML) statements. Additionally, Windows Phone applications cannot use LINQ to SQL to directly access ADO.NET objects. For more information, see LINQ to SQL Support for Windows Phone.

Similarities and Differences

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Similar to a desktop application that uses a SQL Server relational database, a Windows Phone application can use a local database to select, insert, update, and delete data by using LINQ to SQL. This allows your Windows Phone applications to benefit from the powerful query capabilities of LINQ and the storage efficiencies of a relational database. Because a phone has fewer resources than a PC, there are a few ways in which a local database differs from a typical database. These differences include:

• A local database runs in the Windows Phone application’s process. Unlike a client-server database such as Microsoft SQL Server, it does not run continuously as a background service.

• A local database can be accessed only by the corresponding Windows Phone application. Because the database file resides in isolated storage, no other applications can access that data.

• A local database can be accessed only with LINQ to SQL; Transact-SQL is not supported.

Application Deployment

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How to: Deploy a Reference Database with a Windows Phone Application.

To deploy reference data with your application, you need to perform the following steps:

1. Create the helper application: The helper application runs on your development computer, creates the local database in isolated storage, and loads the database with the desired reference data.

2. Extract the local database from the helper application: Use the Isolated Storage Explorer (ISETool.exe) to copy the database from the helper application to a folder on your computer. For more information about the Isolated Storage Explorer, see How to: Use the Isolated Storage Explorer Tool.

3. Create the primary application: Create the application that will consume the reference data.

4. Add the reference data to the primary application: Use Visual Studio to add the local database file to the primary application from the folder where you saved it on your computer. To minimize the size of the application’s assembly, store the file as Content.

After a local database is deployed with an application, it resides in the installation folder in a read-only state. The installation folder is different than isolated storage. To address the database file in this location, use the appdata: prefix. For an example of using this prefix with the database connection string, see Local Database Connection Strings for Windows Phone.

To modify the database containing the reference data, move it out of the installation folder and save it in isolated storage before attempting database changes. To move the database file, you can perform a stream-based copy with the Application.GetResourceStream method to create a stream from the installation folder, and the IsolatedStorageFileStream.Write method to write the stream to isolated storage. The following example demonstrates how to address a database file in the installation folder when you create a stream object.

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, UriKind.Relative)).Stream;

Defining the Data Context

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To create a local database, you must first define the data context and the entities. These classes define the mapping between the object model of the data and the schema of the database. The object-relational capabilities of LINQ to SQL depend on these mapping details to create a relational database that maps to the corresponding data context.

For each entity, mapping details are specified by using LINQ to SQL mapping attributes. These attributes specify database-specific features such as tables, columns, primary keys, and indexes. For more information, see Attribute-based Mapping (LINQ to SQL).  For example, the following code shows a data context named ToDoDataContext and the beginning of an entity class named ToDoItem.

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class ToDoDataContext : DataContext { // Specify the connection string as a static, used in main page and app.xaml. public static string DBConnectionString = "Data Source=isostore:/ToDo.sdf"; // Pass the connection string to the base class. public ToDoDataContext(string connectionString): base(connectionString) { } // Specify a single table for the to-do items. public Table<ToDoItem> ToDoItems; } // Define the to-do items database table. [Table] public class ToDoItem : INotifyPropertyChanged, INotifyPropertyChanging { // Define ID: private field, public property, and database column. private int _toDoItemId; [Column(IsPrimaryKey = true, IsDbGenerated = true, DbType = "INT NOT NULL Identity", CanBeNull = false, AutoSync = AutoSync.OnInsert)] public int ToDoItemId { get { return _toDoItemId; } set { if (_toDoItemId != value) { NotifyPropertyChanging("ToDoItemId"); _toDoItemId = value; NotifyPropertyChanged("ToDoItemId"); } } } . . . . . . . . .

Note:
This is only a portion of the data context code. For a step-by-step walkthrough of creating an application that uses a local database, see How to: Create a Basic Local Database Application for Windows Phone.

To use local database features in your code, you will need the following directives at the top of your code file.

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using System.Data.Linq; using System.Data.Linq.Mapping; using Microsoft.Phone.Data.Linq; using Microsoft.Phone.Data.Linq.Mapping;

Some common LINQ to SQL mapping attributes are shown in the following table. For a full list, see System.Data.Linq.Mapping Namespace.

Attribute	Example	Description
TableAttribute	[Table]	Designates a class as an entity class that is associated with a database table.
ColumnAttribute	[Column(IsPrimaryKey = true)]	Associates a class with a column in a database table. IsPrimaryKey specifies the primary key, for which an index is created by default.
IndexAttribute	[Index(Columns="Column1,Column2 DESC", IsUnique=true, Name="MultiColumnIndex")]	Written at the table level, designates additional indexes on the table. Each index can cover one or more columns.
AssociationAttribute	[Association(Storage="ThisEntityRefName", ThisKey="ThisEntityID", OtherKey="TargetEntityID")]	Designates a property to represent an association, such as a foreign key to primary key association.