Db4O - 我可以保存字符串吗？
我有以下代码：
Assert.IsTrue(Repository.FindAll<string>().Count() == 0);
string newString = "New String";
Repository.Save(newString);
Assert.IsTrue(Repository.FindAll<string>().Count() == 1);
但它失败了。我想这与我保存字符串有关。
我的 Save() 代码是这样的：
public void Save<T>(T obj)
{
if (obj == null)
throw new ArgumentNullException("obj not allowed to be null");
Db.Store(obj);
Db.Commit();
}
我的持久类应该有一些特别的东西吗？或者我可以用 db4o 保存几乎所有东西？
I have the following code:
Assert.IsTrue(Repository.FindAll<string>().Count() == 0);
string newString = "New String";
Repository.Save(newString);
Assert.IsTrue(Repository.FindAll<string>().Count() == 1);
But it is failing. I suppose it has something to do with the fact that I'm saving a string.
My Save() code is this:
public void Save<T>(T obj)
{
if (obj == null)
throw new ArgumentNullException("obj not allowed to be null");
Db.Store(obj);
Db.Commit();
}
Should my persistent classes have something special? Or I can just save pretty much anything with db4o?
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评论（1）
据我所知，平台基元，即使它们可能是引用类型（如 System.String），也只有在实例是另一个对象的子对象（即在字段中引用）时才会被存储，然后该对象才会被存储。因此，在 C# 或 Java 中对原语调用 Store() 不会保存它。基本上，您需要创建一个实体来引用您的字符串才能保存它们；与您需要创建表以将字符串保存到 RDBMS 的方式大致相同。
public class StringEntity { private readonly string value; public StringEntity(string value) : base() { this.value = value; } } ... Assert.IsTrue(Repository.FindAll<StringEntity>().Count() == 0); Repository.Save(new StringEntity("New String")); Assert.IsTrue(Repository.FindAll<StringEntity>().Count() == 1);编辑：
或者更好
public class Primitive<T> { private readonly T value; public Primitive(T value) : base() { this.value = value; } } ... Assert.IsTrue(Repository.FindAll<Primitive<string>>().Count() == 0); Repository.Save(new Primitive<string>("New String")); Assert.IsTrue(Repository.FindAll<Primitive<string>>().Count() == 1);As far as I know, platform primitives, even though they may be reference types (like System.String), will only be stored if an instance is a child of another object (i.e. referenced in a field) and then that object is stored. Therefore, calling Store() on a primitive in C# or Java will not save it. Basically, you'll need to create an entity to reference your strings in order to save them; much the same way as you'd need to create a table in order to save strings to an RDBMS.
public class StringEntity { private readonly string value; public StringEntity(string value) : base() { this.value = value; } } ... Assert.IsTrue(Repository.FindAll<StringEntity>().Count() == 0); Repository.Save(new StringEntity("New String")); Assert.IsTrue(Repository.FindAll<StringEntity>().Count() == 1);EDIT:
or better yet
public class Primitive<T> { private readonly T value; public Primitive(T value) : base() { this.value = value; } } ... Assert.IsTrue(Repository.FindAll<Primitive<string>>().Count() == 0); Repository.Save(new Primitive<string>("New String")); Assert.IsTrue(Repository.FindAll<Primitive<string>>().Count() == 1);