有Basket，存储List<Fruit>。每个Fruit都有一个Pip。如果我存储此关系并稍后检索，ForeignKey PipId有一个值，但对象Pip为null，尽管我使用CascadeRead。< / p>
如果我尝试在CascadeOperation.All上使用FruitList，我会Constraint
at SQLite.PreparedSqlLiteInsertCommand.ExecuteNonQuery (System.Object[] source) [0x00116] in /Users/fak/Dropbox/Projects/sqlite-net/src/SQLite.cs:2507
at SQLite.SQLiteConnection.Insert (System.Object obj, System.String extra, System.Type objType) [0x0014b] in /Users/fak/Dropbox/Projects/sqlite-net/src/SQLite.cs:1386
at SQLite.SQLiteConnection.Insert (System.Object obj) [0x00008] in /Users/fak/Dropbox/Projects/sqlite-net/src/SQLite.cs:1224
at SQLiteNetExtensions.Extensions.WriteOperations.InsertElement (SQLite.SQLiteConnection conn, System.Object element, System.Boolean replace, System.Reflection.PropertyInfo primaryKeyProperty, System.Boolean isAutoIncrementPrimaryKey, System.Collections.Generic.ISet`1[T] objectCache) [0x0005a] in C:\home\mk\work\frameworks\sqlite-net-extensions\SQLiteNetExtensions\Extensions\WriteOperations.cs:270
at SQLiteNetExtensions.Extensions.WriteOperations.InsertElements (SQLite.SQLiteConnection conn, System.Collections.IEnumerable elements, System.Boolean replace, System.Collections.Generic.ISet`1[T] objectCache) [0x00069] in C:\home\mk\work\frameworks\sqlite-net-extensions\SQLiteNetExtensions\Extensions\WriteOperations.cs:238
at SQLiteNetExtensions.Extensions.WriteOperations.InsertValue (SQLite.SQLiteConnection conn, System.Object value, System.Boolean replace, System.Boolean recursive, System.Collections.Generic.ISet`1[T] objectCache) [0x0002c] in C:\home\mk\work\frameworks\sqlite-net-extensions\SQLiteNetExtensions\Extensions\WriteOperations.cs:219
at SQLiteNetExtensions.Extensions.WriteOperations.InsertChildrenRecursive (SQLite.SQLiteConnection conn, System.Object element, System.Boolean replace, System.Boolean recursive, System.Collections.Generic.ISet`1[T] objectCache) [0x0004c] in C:\home\mk\work\frameworks\sqlite-net-extensions\SQLiteNetExtensions\Extensions\WriteOperations.cs:200
at SQLiteNetExtensions.Extensions.WriteOperations.InsertWithChildrenRecursive (SQLite.SQLiteConnection conn, System.Object element, System.Boolean replace, System.Boolean recursive, System.Collections.Generic.ISet`1[T] objectCache) [0x0002b] in C:\home\mk\work\frameworks\sqlite-net-extensions\SQLiteNetExtensions\Extensions\WriteOperations.cs:181
at SQLiteNetExtensions.Extensions.WriteOperations.InsertWithChildren (SQLite.SQLiteConnection conn, System.Object element, System.Boolean recursive) [0x00000] in C:\home\mk\work\frameworks\sqlite-net-extensions\SQLiteNetExtensions\Extensions\WriteOperations.cs:59
at SQLiteNetExtensionsAsync.Extensions.WriteOperations+<>c__DisplayClass1_0.<InsertWithChildrenAsync>b__0 () [0x00013] in C:\home\mk\work\frameworks\sqlite-net-extensions\SQLiteNetExtensionsAsync-PCL\Extensions\WriteOperations.cs:55
at System.Threading.Tasks.Task.InnerInvoke () [0x0000f] in <d18287e1d683419a8ec3216fd78947b9>:0
at System.Threading.Tasks.Task.Execute () [0x00010] in <d18287e1d683419a8ec3216fd78947b9>:0
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw () [0x0000c] in <d18287e1d683419a8ec3216fd78947b9>:0
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess (System.Threading.Tasks.Task task) [0x0003e] in <d18287e1d683419a8ec3216fd78947b9>:0
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification (System.Threading.Tasks.Task task) [0x00028] in <d18287e1d683419a8ec3216fd78947b9>:0
at System.Runtime.CompilerServices.TaskAwaiter.ValidateEnd (System.Threading.Tasks.Task task) [0x00008] in <d18287e1d683419a8ec3216fd78947b9>:0
at System.Runtime.CompilerServices.TaskAwaiter.GetResult () [0x00000] in <d18287e1d683419a8ec3216fd78947b9>:0
at TestSQLite.Database+<StoreBasketAsync>d__5.MoveNext () [0x0021b] in C:\Users\some-user\Documents\Visual Studio 2015\Projects\TestSQLite\TestSQLite\TestSQLite\Database.cs:189
此外，我尝试在recursive: true上使用InsertWithChildrenAsync()，但Pip也是null。这是一个例子：
数据模型
public class Basket
{
private string number;
private List<Fruit> fruitList;
[PrimaryKey]
public string Number
{
get { return this.number; }
set { this.number = value; }
}
public string Name { get; set; }
[OneToMany(CascadeOperations = CascadeOperation.CascadeRead)]
public List<Fruit> FruitList
{
get { return this.fruitList; }
set { this.fruitList = value; }
}
public Basket()
{
}
}
public class Fruit
{
private string number;
private Pip pip;
[PrimaryKey]
public string Number
{
get { return this.number; }
set { this.number = value; }
}
public string Type { get; set;}
[ForeignKey(typeof(Pip))]
public string PipId { get; set; }
[OneToOne]
public Pip Pip
{
get { return this.pip; }
set { this.pip = value; }
}
[ForeignKey(typeof(Basket))]
public string BasketId { get; set; }
public Fruit()
{
}
}
public class Pip
{
private string number;
private string title;
[PrimaryKey]
public string Number
{
get { return this.number; }
set { this.number = value; }
}
public string Title
{
get { return this.title; }
set { this.title = value; }
}
public Pip()
{
}
}
数据库操作
public class Database
{
private readonly SQLiteAsyncConnection database;
public Database(string databasePath)
{
this.database = new SQLiteAsyncConnection(databasePath);
this.database.CreateTableAsync<Basket>().Wait();
this.database.CreateTableAsync<Fruit>().Wait();
this.database.CreateTableAsync<Pip>().Wait();
}
public async Task<Basket> GetBasketAsync(string basketId)
{
try
{
var queryResult = await this.database.Table<Basket>().Where(b => b.Number == basketId).CountAsync();
if (queryResult > 0)
{
return await this.database.GetWithChildrenAsync<Basket>(basketId, true);
}
else
{
return null;
}
}
catch(Exception ex)
{
System.Diagnostics.Debug.WriteLine(ex.Message);
return null;
}
}
public async Task<Fruit> GetFruitAsync(string number)
{
try
{
var queryResult = await this.database.Table<Fruit>().Where(f => f.Number == number).CountAsync();
if (queryResult > 0)
{
return await this.database.GetWithChildrenAsync<Fruit>(number, true);
}
else
{
return null;
}
}
catch(Exception ex)
{
System.Diagnostics.Debug.WriteLine(ex.Message);
return null;
}
}
public async Task<Pip> GetPipAsync(string number)
{
try
{
var queryResult = await this.database.Table<Pip>().Where(p => p.Number == number).CountAsync();
if (queryResult > 0)
{
return await this.database.GetAsync<Pip>(number);
}
else
{
return null;
}
}
catch(Exception ex)
{
System.Diagnostics.Debug.WriteLine(ex.Message);
return null;
}
}
public async Task StoreBasketAsync(Basket basket)
{
if (basket == null)
return;
try
{
await this.StoreFruitListAsync(basket.FruitList);
var foundItem = await this.GetBasketAsync(basket.Number);
if (foundItem != null)
{
await this.database.UpdateWithChildrenAsync(basket);
}
else
{
await this.database.InsertWithChildrenAsync(basket);
}
}
catch (Exception ex)
{
System.Diagnostics.Debug.WriteLine(ex.Message);
}
}
public async Task StoreFruitListAsync(List<Fruit> fruitList)
{
if (fruitList == null || fruitList.Count == 0)
return;
try
{
foreach (Fruit fruit in fruitList)
{
await this.StorePipAsync(fruit.Pip);
var foundItem = await this.GetFruitAsync(fruit.Number);
if (foundItem != null)
{
await this.database.UpdateWithChildrenAsync(fruit);
}
else
{
await this.database.InsertWithChildrenAsync(fruit);
}
}
}
catch (Exception ex)
{
System.Diagnostics.Debug.WriteLine(ex.Message);
}
}
public async Task<int> StorePipAsync(Pip pip)
{
if (pip == null)
return 0;
try
{
var foundItem = await this.GetPipAsync(pip.Number);
if (foundItem != null)
{
return await this.database.UpdateAsync(pip);
}
else
{
return await this.database.InsertAsync(pip);
}
}
catch (Exception ex)
{
System.Diagnostics.Debug.WriteLine(ex.Message);
return 0;
}
}
}
测试用例
public MainPage()
{
InitializeComponent();
Pip pip = new Pip();
pip.Number = "4";
pip.Title = "pip from apple";
Fruit apple = new Fruit();
apple.Number = "1";
apple.Pip = pip;
Basket basket = new Basket();
basket.Number = "10";
basket.Name = "grandma";
basket.FruitList = new List<Fruit>() { apple };
this.basket = basket;
}
protected override async void OnAppearing()
{
base.OnAppearing();
await App.Database.StoreBasketAsync(this.basket);
Basket existingBasket = await App.Database.GetBasketAsync(this.basket.Number);
}
我正在使用最新的SQLiteNetExtensions.Async v2.0.0-alpha2 NuGet包。如何正确检索子元素Pip？
答案 0 :(得分：1)
现在我读了documentation并说明了
级联读取操作允许您从正在获取的对象开始从数据库中获取完整的关系树，并继续
CascadeOperations设置为CascadeRead的所有关系
我的Fruit课程现在看起来像这样
public class Fruit
{
[OneToOne(CascadeOperations = CascadeOperation.CascadeRead)]
public Pip Pip
{
get { return this.pip; }
set { this.pip = value; }
}
}
它按预期工作。我想，CascadeRead只有在我有一个object时才需要，它有一些进一步的关系，但事实并非如此。对于所有对象都需要CascadeRead，无论对象是如何构建的，都应该递归获取。