Constraint

All Known Subinterfaces:

Constraints

All Known Implementing Classes:

QCon, QConClass, QConEvaluation, QConJoin, QConObject, QConPath, QConstraints, QConUnconditional
```
public interface Constraint
```
constraint to limit the objects returned upon query execution.

Constraints are constructed by calling Query.constrain(Object).

Constraints can be joined with the methods and(com.db4o.query.Constraint) and or(com.db4o.query.Constraint).

The methods to modify the constraint evaluation algorithm may be merged, to construct combined evaluation rules. Examples:
- Constraint#smaller().equal() for "smaller or equal"
- Constraint#not().like() for "not like"
- Constraint#not().greater().equal() for "not greater or equal"

Method Summary

Methods
Modifier and Type	Method and Description
`Constraint`	`and(Constraint with)` links two Constraints for AND evaluation.
`Constraint`	`byExample()` set the evaluation mode to object comparison (query by example).
`Constraint`	`contains()` sets the evaluation mode to string contains comparison.
`Constraint`	`endsWith(boolean caseSensitive)` sets the evaluation mode to string endsWith comparison.
`Constraint`	`equal()` Used in conjunction with `smaller()` or `greater()` to create constraints like "smaller or equal", "greater or equal".
`java.lang.Object`	`getObject()` returns the Object the query graph was constrained with to create this `Constraint`.
`Constraint`	`greater()` sets the evaluation mode to `>`.
`Constraint`	`identity()` sets the evaluation mode to identity comparison.
`Constraint`	`like()` sets the evaluation mode to "like" comparison.
`Constraint`	`not()` turns on not() comparison.
`Constraint`	`or(Constraint with)` links two Constraints for OR evaluation.
`Constraint`	`smaller()` sets the evaluation mode to `<`.
`Constraint`	`startsWith(boolean caseSensitive)` sets the evaluation mode to string startsWith comparison.

- Method Detail
  - and
```
Constraint and(Constraint with)
```
    links two Constraints for AND evaluation. For example:
    query.constrain(Pilot.class);
    query.descend("points").constrain(101).smaller().and(query.descend("name").constrain("Test Pilot0"));
    will retrieve all pilots with points less than 101 and name as "Test Pilot0"
    
    Parameters:
    with - the other Constraint
    
    Returns:
    a new Constraint, that can be used for further calls to and(Constraint) and or(Constraint)
  - or
```
Constraint or(Constraint with)
```
    links two Constraints for OR evaluation. For example:
    
    query.constrain(Pilot.class);
    query.descend("points").constrain(101).greater().or(query.descend("name").constrain("Test Pilot0"));
    will retrieve all pilots with points more than 101 or pilots with the name "Test Pilot0"
    
    Parameters:
    with - the other Constraint
    
    Returns:
    a new Constraint, that can be used for further calls to and(Constraint) and or(Constraint)
  - equal
```
Constraint equal()
```
    Used in conjunction with smaller() or greater() to create constraints like "smaller or equal", "greater or equal". For example:
    query.constrain(Pilot.class);
    query.descend("points").constrain(101).smaller().equal();
    will return all pilots with points <= 101.
    
    Returns:
    this Constraint to allow the chaining of method calls.
  - greater
```
Constraint greater()
```
    sets the evaluation mode to >. For example:
    query.constrain(Pilot.class);
    query.descend("points").constrain(101).greater()
    will return all pilots with points > 101.
    
    Returns:
    this Constraint to allow the chaining of method calls.
  - smaller
```
Constraint smaller()
```
    sets the evaluation mode to <. For example:
    query.constrain(Pilot.class);
    query.descend("points").constrain(101).smaller()
    will return all pilots with points < 101.
    
    Returns:
    this Constraint to allow the chaining of method calls.
  - identity
```
Constraint identity()
```
    sets the evaluation mode to identity comparison. In this case only objects having the same database identity will be included in the result set. For example:
    Pilot pilot = new Pilot("Test Pilot1", 100);
    Car car = new Car("BMW", pilot);
    container.store(car);
    // Change the name, the pilot instance stays the same
    pilot.setName("Test Pilot2");
    // create a new car
    car = new Car("Ferrari", pilot);
    container.store(car);
    Query query = container.query();
    query.constrain(Car.class);
    // All cars having pilot with the same database identity
    // will be retrieved. As we only created Pilot object once
    // it should mean all car objects
    query.descend("_pilot").constrain(pilot).identity();
    
    Returns:
    this Constraint to allow the chaining of method calls.
  - byExample
```
Constraint byExample()
```
    set the evaluation mode to object comparison (query by example).
    
    Returns:
    this Constraint to allow the chaining of method calls.
  - like
```
Constraint like()
```
    sets the evaluation mode to "like" comparison. This mode will include all objects having the constrain expression somewhere inside the string field. For example:
    Pilot pilot = new Pilot("Test Pilot1", 100);
    container.store(pilot);
    ...
    query.constrain(Pilot.class);
    // All pilots with the name containing "est" will be retrieved
    query.descend("name").constrain("est").like();
    
    Returns:
    this Constraint to allow the chaining of method calls.
  - contains
```
Constraint contains()
```
    sets the evaluation mode to string contains comparison. The contains comparison is case sensitive. For example:
    Pilot pilot = new Pilot("Test Pilot1", 100);
    container.store(pilot);
    ...
    query.constrain(Pilot.class);
    // All pilots with the name containing "est" will be retrieved
    query.descend("name").constrain("est").contains();
    
    Returns:
    this Constraint to allow the chaining of method calls.
    See Also:
    like() for case insensitive string comparison
  - startsWith
```
Constraint startsWith(boolean caseSensitive)
```
    sets the evaluation mode to string startsWith comparison. For example:
    Pilot pilot = new Pilot("Test Pilot0", 100);
    container.store(pilot);
    ...
    query.constrain(Pilot.class);
    query.descend("name").constrain("Test").startsWith(true);
    
    Parameters:
    caseSensitive - comparison will be case sensitive if true, case insensitive otherwise
    
    Returns:
    this Constraint to allow the chaining of method calls.
  - endsWith
```
Constraint endsWith(boolean caseSensitive)
```
    sets the evaluation mode to string endsWith comparison. For example:
    Pilot pilot = new Pilot("Test Pilot0", 100);
    container.store(pilot);
    ...
    query.constrain(Pilot.class);
    query.descend("name").constrain("T0").endsWith(false);
    
    Parameters:
    caseSensitive - comparison will be case sensitive if true, case insensitive otherwise
    
    Returns:
    this Constraint to allow the chaining of method calls.
  - not
```
Constraint not()
```
    turns on not() comparison. All objects not fullfilling the constrain condition will be returned. For example:
    Pilot pilot = new Pilot("Test Pilot1", 100);
    container.store(pilot);
    ...
    query.constrain(Pilot.class);
    query.descend("name").constrain("t0").endsWith(true).not();
    
    Returns:
    this Constraint to allow the chaining of method calls.
  - getObject
```
java.lang.Object getObject()
```
    returns the Object the query graph was constrained with to create this Constraint.
    
    Returns:
    Object the constraining object.

Interface Constraint

Method Summary

Method Detail

and

or

equal

greater

smaller

identity

byExample

like

contains

startsWith

endsWith

not

getObject