JDO : JDOQL Methods

When writing the "filter" for a JDOQL Query you can make use of some methods on the various Java types. The range of methods included as standard in JDOQL is not as flexible as with the true Java types, but the ones that are available are typically of much use. While DataNucleus supports all of the methods in the JDO standard, it also supports several yet to be standardised (extension) method. In addition, some datastores have support for methods more appropriate to their environment, for example for RDBMS



String Methods
Method Description Standard
startsWith(String) Returns if the string starts with the passed string
endsWith(String) Returns if the string ends with the passed string
indexOf(String) Returns the first position of the passed string
indexOf(String,int) Returns the position of the passed string, after the passed position
substring(int) Returns the substring starting from the passed position
substring(int,int) Returns the substring between the passed positions
toLowerCase() Returns the string in lowercase
toUpperCase() Retuns the string in UPPERCASE
matches(String pattern) Returns whether string matches the passed expression. The pattern argument follows the rules of java.lang.String.matches method.
charAt(int) Returns the character at the passed position
startsWith(String, int) Returns if the string starts with the passed string, from the passed position
length() Returns the length of the string
trim() Returns a trimmed version of the string
equals(String) Returns if the strings are equal
equalsIgnoreCase(String) Returns if the strings are equal ignoring case
replaceAll(String, String) Returns the string with all instances of str1 replaced by str2

Here's an example using a Product class, looking for objects which their abreviation is the beginning of a trade name. The trade name is provided as parameter. 

Declarative JDOQL :
Query query = pm.newQuery(mydomain.Product.class);
query.setFilter(":tradeName.startsWith(this.abbreviation)");
List results = (List)query.execute("Workbook Advanced");

Single-String JDOQL :
Query query = pm.newQuery(
    "SELECT FROM mydomain.Product " +
    "WHERE :tradeName.startsWith(this.abbreviation)");
List results = (List)query.execute("Workbook Advanced");


Collection Methods
Method Description Standard
isEmpty() Returns whether the collection is empty
contains(value) Returns whether the collection contains the passed element
size() Returns the number of elements in the collection
get(int) Returns the element at that position of the List

Here's an example demonstrating use of contains(). We have an Inventory class that has a Collection of Product objects, and we want to find the Inventory objects with 2 particular Products in it. Here we make use of a variable ( prd to represent the Product being contained 

Declarative JDOQL :
Query query = pm.newQuery(mydomain.Inventory.class);
query.setFilter("products.contains(prd) && (prd.name==\"product 1\" || prd.name==\"product 2\")");
List results = (List)query.execute();

Single-String JDOQL:
Query query = pm.newQuery(
    "SELECT FROM mydomain.Inventory EXCLUDE SUBCLASSES " + 
    "WHERE products.contains(prd) && (prd.name==\"product 1\" || prd.name==\"product 2\")");
List results = (List)query.execute();


Map Methods
Method Description Standard
isEmpty() Returns whether the map is empty
containsKey(key) Returns whether the map contains the passed key
containsValue(value) Returns whether the map contains the passed value
get(key) Returns the value from the map with the passed key
size() Returns the number of entries in the map
containsEntry(key, value) Returns whether the map contains the passed entry

Here's an example using a Product class as a value in a Map. Our example represents an organisation that has several Inventories of products. Each Inventory of products is stored using a Map, keyed by the Product name. The query searches for all Inventories that contain a product with the name "product 1". 

Declarative JDOQL :
Query query = pm.newQuery(mydomain.Inventory.class, "products.containsKey(\"product 1\")");
List results = (List)query.execute();

Single-String JDOQL :
Query query = pm.newQuery(
    "SELECT FROM mydomain.Inventory EXCLUDE SUBCLASSES " +
    "WHERE products.containsKey(\"product 1\")");
List results = (List)query.execute();

Here's the source code for reference 

class Inventory
{
    Map<String, Product> products;
    ...
}
class Product
{
    ...
}


Temporal Methods
Method Description Standard
getDay() Returns the day (of the month) for the date (java.util.Date types)
getMonth() Returns the month for the date (java.util.Date types)
getYear() Returns the year for the date (java.util.Date types)
getHour() Returns the hour for the time (java.util.Date types)
getMinute() Returns the minute for the time (java.util.Date types)
getSecond() Returns the second for the time (java.util.Date types)


Enum Methods
Method Description Standard
ordinal() Returns the ordinal of the enum (not implemented for enum expression when persisted as a string)
toString() Returns the string form of the enum (not implemented for enum expression when persisted as a numeric)


Other Methods
Method Description Standard
Math.abs(number) Returns the absolute value of the passed number
Math.sqrt(number) Returns the square root of the passed number
Math.cos(number) Returns the cosine of the passed number
Math.sin(number) Returns the absolute value of the passed number
Math.tan(number) Returns the tangent of the passed number
Math.acos(number) Returns the arc cosine of the passed number
Math.asin(number) Returns the arc sine of the passed number
Math.atan(number) Returns the arc tangent of the passed number
Math.ceil(number) Returns the ceiling of the passed number
Math.exp(number) Returns the exponent of the passed number
Math.floor(number) Returns the floor of the passed number
Math.log(number) Returns the log(base e) of the passed number
JDOHelper.getObjectId(object) Returns the object identity of the passed persistent object
JDOHelper.getVersion(object) Returns the version of the passed persistent object