The Object Values API is the third query type that NeoDatis ODB supports.
The Object Values API is a very powerful API to let one retrieve values of object attributes instead of the full object itself!
Sometime, you just need to retrieve the name of a user (to build a combo, for example), and traditional Object Databases force you to retrieve the whole object. NeoDatis ODB let you retrieve the attributes you need without needing instancianting a single object. This leverage a very fast and powerfull API for building reports for example.
Check a single code snippet to check how it work:
ODB odb = open("values.odb"); odb.store(new User("user1","email1",new Profile("profile name",new Function("f111")))); odb.close(); odb = open("values.odb"); Values values = odb.getValues(new ValuesCriteriaQuery(User.class).field("name")); IObjectValues ov = values.nextValues(); System.out.println("user1", ov.getByAlias("name")); System.out.println("user1", ov.getByIndex(0)); odb.close();
As a user have a profile and the profile has a name, you may want to retrieve the name of the profile directly, like this:
Values values = odb.getValues(new ValuesCriteriaQuery(User.class).field("name").field("profile.name"));
Object Values API provides more features to query object values like:
- sum
- average
- min
- max
- count
- group by
- Custom function
Sum
Values values = odb.getValues(new ValuesCriteriaQuery(TestClass.class).sum("int1","sum of int1")
Average
Values values = odb.getValues(new ValuesCriteriaQuery(TestClass.class).avg("int1","average of int1")
Min & Max
Values values = odb.getValues(new ValuesCriteriaQuery(TestClass.class) .min("int1","min of int1") .max("int1","max of int1");
Count
Values values = odb.getValues(new ValuesCriteriaQuery(TestClass.class).count("my count");
Custom function
If you need a specific function, you can always implement you own Action do compute what you need. This is done by extending the
CustomQueryFieldAction class.
Here is a simple implementation example:
package org.neodatis.odb.test.query.values; import java.math.BigDecimal; import org.neodatis.odb.core.OID; import org.neodatis.odb.core.io.AttributeValuesMap; import org.neodatis.odb.core.query.values.CustomQueryFieldAction; import org.neodatis.odb.core.query.values.ValuesUtil; public class TestCustomQueryFieldAction extends CustomQueryFieldAction { private BigDecimal myValue; public TestCustomQueryFieldAction() { this.myValue = new BigDecimal(0); } public void execute(final OID oid, final AttributeValuesMap values) { Number n = ValuesUtil.convert((Number) values.get(attributeName)); myValue = myValue.add(new BigDecimal(n.toString()).multiply(new BigDecimal(2))); } public Object getValue() { return myValue; } public boolean isMultiRow() { return false; } public void start() { // Nothing to do } public void end() { // Nothing to do } }
And here is how you use this custom funcion:
ICustomQueryFieldAction custom = new TestCustomQueryFieldAction(); Values values = odb.getValues(new ValuesCriteriaQuery(TestClass.class) .custom("int1", "custom of int1",custom));
