08，Windows Phone 本地存储

内容预告：

• Windows Phone 的数据库支持
• LINQ to SQL
• 性能和最佳实践

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LINQ to Everything:

支持复杂的结构：

支持外键：

WebService缓存：

本地存储：

架构：

对象：

定义表：

  // Define the tables in the database  [Table]  public class Wine : INotifyPropertyChanged, INotifyPropertyChanging  {      private string wineID;      private string name;      [Column(IsPrimaryKey=true)]      public string WineID       {          get { return wineID; }         set {             InvokePropertyChanging(new PropertyChangingEventArgs("WineID"));             wineID = value;             InvokePropertyChanged(new PropertyChangedEventArgs("WineID"));         }         }      [Column]      public string Name { ... }      ...}

定义数据上下文：

// Define the data context.public partial class WineDataContext : DataContext {public Table<Wine> Wines;public Table<Vineyard> Vineyards;public WineDataContext(string connection) : base(connection) { }}...// Create the database from data context, using a connection stringDataContext db = new WineDataContext("isostore:/wineDB.sdf");if (!db.DatabaseExists())     db.CreateDatabase();

用SQLMetal代码生成工具:

c:\>Sqlmetal /code:northwindEntities.cs                   /context:NorthwindDataContext                  /pluralize northwind.sdf

查询：

 // Create the database form data context, using a connection string DataContext db = new WineDataContext("isostore:/wineDB.sdf"); // Find all wines currently at home, ordered by date acquired var q =  from w in db.Wines       where w.Varietal.Name == “Shiraz” && w.IsAtHome == true       orderby w.DateAcquired       select w;

插入，更新，删除：别忘了submitChanges

插入：

Wine newWine = new Wine{WineID = “1768",Name = “Windows Phone Syrah",Description = “Bold and spicy"};db.Wines.InsertOnSubmit(newWine);db.SubmitChanges();

更新：

Wine wine = (from w in db.Wines where w.WineID == “1768" select w).First();wine.Description = “Hints of plum and melon";db.SubmitChanges();

删除：

var vineyardsToDelete = from Vineyards v in db.Vineyardswhere v.Country == “Australia”select v;db.Vineyards.DeleteAllOnSubmit(vineyardsToDelete);            db.SubmitChanges();

更新数据库结构：

WineDataContext wineDC = new WineDataContext(App.WineDBConnectionString);DatabaseSchemaUpdater dsu = wineDC.CreateDatabaseSchemaUpdater();if (dsu.DatabaseSchemaVersion == 1){dsu.AddColumn<Wine>("BottleType");dsu.DatabaseSchemaVersion = 2;dsu.Execute();} 

性能和最佳实践：

• 保持修改的集合很小，换句话说，尽早提交修改，以避免程序终止时数据丢失。
• 用后台线程。
• 优化只读查询。
• 提前填充大量数据。
• 用对的工具，大量复杂的数据用数据库，小数据用独立存储。