A dynamic finder method is a finder method for which you don't need to write a JPA query. It fetches entity instances from the database based on one or more persistent fields of the entity class. The implementation of these dynamic finder methods is auto-generated by Roo when you add their names to a persistent entity. As Roo doesn't create a DAO layer of an application, dynamic finder methods are defined in the entity class. In this recipe, we will look at the finder list command, which introspects a persistent entity and suggests names of possible dynamic finder methods that can be added to the given persistent entity.
Create a sub-directory ch03-recipes inside the C:
oo-cookbook directory.
Execute the ch03_persistent_entities.roo script to create a flight-app Roo project. The script sets up Hibernate as a persistence provider and creates a Flight entity, which has FlightKey as its composite primary key class. Additionally, the script adds fields to the Flight and FlightKey classes. If you are using a different database than MySQL or your connection settings are different than what is specified in the script, then modify the script accordingly.
Start Roo shell from the C:
oo-cookbookch03-recipes directory.
To use the finder list command to view dynamic finder methods, follow the given steps:
- Set the focus of the subsequent commands on the
Flightentity using thefocuscommand:roo> focus --class ~.domain.Flight - Execute the
finderlistcommand to view the list of candidate dynamic finder methods for theFlightentity, as shown here:~.domain.Flight roo> finder list ..... findFlightsByCreatedDateBetween(Date minCreatedDate, Date maxCreatedDate) findFlightsByCreatedDateGreaterThan(Date createdDate) ..... findFlightsByDestination(String destination) findFlightsByDestinationEquals(String destination) findFlightsByDestinationIsNotNull() findFlightsByDestinationIsNull() findFlightsByDestinationLike(String destination) findFlightsByDestinationNotEquals(String destination)
The finder list command displays names of the candidate dynamic finder methods for an entity. By default, the dynamic finder methods suggested by the finder list command search for entity instances based on only one persistent field of the entity. For instance, in the output of the finder list command you will not find a dynamic finder method name which finds the Flight entity instances based on both the createdDate and modifiedDate fields. If an entity inherits from a mapped superclass, then the dynamic finder methods corresponding to the inherited fields are also displayed by Roo.
The dynamic finder methods suggested by the finder list command are dependent upon the type of the field. For instance, the createdDate is of type java.util.Date and can participate in greater than, less than, and between comparisons; therefore, findFlightsByCreatedDateBetween, findFlightsByCreatedDateGreaterThan, and so on, are shown as candidate dynamic finder methods, and these methods accept the createdDate field as the argument. On the other hand, the destination field is of type String, which doesn't participate in greater than, less than, and between comparisons; therefore, Roo doesn't suggest dynamic finder methods for finding the Flight instances based on greater than, less than, and between comparisons of destination field.
Let's now look at how to instruct Roo to:
- Provide a list of candidate dynamic finder methods, which fetch entities based on more than one persistent field
- Restrict suggested dynamic finder method names based on a filter criteria
If you want Roo to list finder method names that fetch entities based on multiple persistent fields, you should use the depth argument of the finder list command. The depth argument accepts a numeric value, which determines the number of persistent fields the dynamic finder method uses to search for entities in the database. For instance, if you want Flight instances to be searched based on both the origin and destination fields, then the value of the depth argument must be 2. The default value of the depth argument is 1, therefore; when we executed the finder list command, without specifying depth argument, it listed dynamic finder method names that fetch entities based on only one persistent field. The following finder list command shows the affect of the depth argument on the suggested list of dynamic finder method names:
~.domain.Flight roo> finder list --depth 2 findFlightsByDestinationAndOrigin(String destination, String origin) findFlightsByDestinationAndOriginEquals(String destination, String origin) .....
As the output suggests, two persistent fields now form part of listed candidate dynamic finder method names. Similarly, if you want your finders to span a n number of persistent fields, then specify n as the value of a depth argument.
As you increase the value of the depth argument, the number of candidate dynamic finder method names listed by Roo increases exponentially due to the number of possible combinations for method arguments. In such cases, it is desired to filter candidate dynamic finder method names based on a filter criteria. The finder list command provides a filter argument, which accepts a comma separated list of strings that must be present in the dynamic finder method name. Dynamic finder method names which don't contain the strings specified by the filter argument are omitted from the displayed list of candidate dynamic finder method names. This makes it easy for you to locate dynamic finder methods that you want to add to a persistent entity.
Tip
Note that there should be no spaces in the comma-separated list of strings specified as the value of the filter argument.
The following finder list command shows the filter argument usage:
~.domain.Flight roo> finder list --depth 2 --filter destinationlike,originlike findFlightsByDestinationLikeAndOriginLike(..) findFlightsByDestinationLikeOrOriginLike(..) findFlightsByOriginLikeAndDestinationLike(..) findFlightsByOriginLikeOrDestinationLike(..)
The output now shows only four methods that contain the text specified in the filter argument. Similarly, you can add additional text to the filter argument to narrow down the list of candidate dynamic finder method names that are displayed by the finder list command.