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

---

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 string
DataContext 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.Vineyards
where 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。