| java.lang.Object
 com.db4o.query.Predicate
All known Subclasses: com.db4o.test.nativequery.ToBeInstrumented, com.db4o.test.nativequery.cats.SodaCatPredicate,
| Predicate | | abstract public class Predicate implements Serializable(Code) | | Base class for native queries.
Native Queries provide the ability to run one or more lines
of code against all instances of a class. Native query expressions should
return true to mark specific instances as part of the result set.
db4o will attempt to optimize native query expressions and run them
against indexes and without instantiating actual objects, where this is
possible.
The syntax of the enclosing object for the native query expression varies
slightly, depending on the language version used. Here are some examples,
how a simple native query will look like in some of the programming languages and
dialects that db4o supports:
// C# .NET 2.0
IList <Cat> cats = db.Query <Cat> (delegate(Cat cat) {
return cat.Name == "Occam";
});
// Java JDK 5
List <Cat> cats = db.query(new Predicate<Cat>() {
public boolean match(Cat cat) {
return cat.getName().equals("Occam");
}
});
// Java JDK 1.2 to 1.4
List cats = db.query(new Predicate() {
public boolean match(Cat cat) {
return cat.getName().equals("Occam");
}
});
// Java JDK 1.1
ObjectSet cats = db.query(new CatOccam());
public static class CatOccam extends Predicate {
public boolean match(Cat cat) {
return cat.getName().equals("Occam");
}
});
// C# .NET 1.1
IList cats = db.Query(new CatOccam());
public class CatOccam : Predicate {
public boolean Match(Cat cat) {
return cat.Name == "Occam";
}
});
Summing up the above:
In order to run a Native Query, you can
- use the delegate notation for .NET 2.0.
- extend the Predicate class for all other language dialects
A class that extends Predicate is required to
implement the #match() / #Match() method, following the native query
conventions:
- The name of the method is "#match()" (Java) / "#Match()" (.NET).
- The method must be public public.
- The method returns a boolean.
- The method takes one parameter.
- The Type (.NET) / Class (Java) of the parameter specifies the extent.
- For all instances of the extent that are to be included into the
resultset of the query, the match method should return true. For all
instances that are not to be included, the match method should return
false.
|
| Method Summary | |
| public boolean | appliesTo(ExtentType candidate)
public for implementation reasons, please ignore. | | public Class<? extends ExtentType> | extentType()
public for implementation reasons, please ignore. | | abstract public boolean | match(ExtentType candidate)
The match method that needs to be implemented by the user. |
| PREDICATEMETHOD_NAME | | final public static String PREDICATEMETHOD_NAME(Code) | | public for implementation reasons, please ignore.
|
| Predicate | | public Predicate()(Code) | | |
| Predicate | | public Predicate(Class<ExtentType> extentType)(Code) | | |
| appliesTo | | public boolean appliesTo(ExtentType candidate)(Code) | | public for implementation reasons, please ignore.
|
| extentType | | public Class<? extends ExtentType> extentType()(Code) | | public for implementation reasons, please ignore.
|
| match | | abstract public boolean match(ExtentType candidate)(Code) | | The match method that needs to be implemented by the user.
Parameters:
candidate - the candidate object passed from db4o true to include an object in the resulting ObjectSet |
|
|