Systems and methods for dynamic querying

Abstract

A user can generate queries dynamically at runtime without having to redeploy the appropriate EJB or hard-code the query into the user application. A properties object can be generated to accept the query settings from the user. These settings can be extracted at runtime when the appropriate finder method is invoked, such that the desired query statement, such as a SQL statement, can be generated and executed against the database.

Description

COPYRIGHT NOTICE

A portion of the disclosure of this patent document contains material which is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document of the patent disclosure, as it appears in the Patent and Trademark Office patent file or records, but otherwise reserves all copyright rights whatsoever.

FIELD OF THE INVENTION

The present invention relates to executing queries against a database.

BACKGROUND

The Enterprise JavaBean (EJB) specification, published by Sun Microsystems, Inc. of Palo Alto, Calif., describes ways in which a user can execute queries against a database, as well as ways in which a user can communicate queries to an EJB container. Presently, the EJB 2.0 specification forces users to hard-code finder queries into a deployment descriptor for an EJB. A user develops a query before deploying the EJB. Once the EJB is deployed, the user is able to execute the query. A problem exists with this approach, however, in that it is necessary to redeploy the EJB every time the user wishes to run a new query.

BRIEF SUMMARY

Systems and methods in accordance with one embodiment of the present invention can allow a user to dynamically generate a query to be executed against a database. A properties object can be generated that holds settings for the query, which can be specified by a user at runtime. When the query is to be executed, the user or application can invoke an appropriate finder method. The server receiving the call from the finder method can extract the user-specified settings from the properties object and parse the finder method in order to generate a query statement. The server can then execute the query statement on the database and return the appropriate results. The generating of the properties object and the query statement can happen at runtime.

Other features, aspects, and objects of the invention can be obtained from a review of the specification, the figures, and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of a system in accordance with one embodiment of the present invention.

FIG. 2 is a flowchart showing the steps of a method that can be used with the system of FIG. 1.

DETAILED DESCRIPTION

Systems and methods in accordance with one embodiment of the present invention can allow a user to define a query programmatically rather than defining the query statically. Static queries are defined, for example, by hard-coding the static query into the deployment descriptor for an EJB. Programmatic queries, or “dynamic queries”, allow users to construct and execute queries in their application code. This can provide several benefits over static queries which utilize static finder methods.

One such benefit is the ability to create and execute new queries without having to update and redeploy an EJB. When deploying an EJB with static queries, each query is read and parsed in order to generate the SQL to be sent to the database. Finder methods can be utilized in executing the query, which can be defined in the home interface of an entity bean. An example of a finder method is findByPrimaryKey( ), which can accept an instance of a primary key and return an instance of that entity type (or throw an exception). Additional finder methods can be defined in local home or remote home interfaces, with each finder method being associated with a query in the deployment descriptor. With dynamic queries, however, the query and corresponding SQL can be generated at runtime.

Another benefit is that the size of an EJB deployment descriptor is reduced. Since the finder queries can be created dynamically, they do not have to be statically defined in the deployment descriptor. For some applications this approach may be a little slower, but the added flexibility will outweigh the slight hit in performance for many users.

One system and method for implementing dynamic queries utilizes the generation of a class such as an ejbHome class. Such a class can be used to implement an extra interface with a method that can execute the query. As shown in FIG. 1, when a user 100 wants to execute a query against a database 112 at runtime, an object such as a Java properties object 104 can be generated that can be populated with the settings for the finder method 106, such as a container-managed or bean-managed finder method. The finder method 106 can then be invoked on the query home of the appropriate EJB 108, which can be stored on a server 110 or EJB container in communication with, and capable of executing SQL queries against, a database 112. Once the call makes it into the server 110, the properties object 104 can be inspected and the user settings extracted. The finder method 106 can be parsed and the SQL query statement generated that is to be sent to the database 112. The query is executed and, depending on the user settings, the use of the results can be determined. One possible result of such a query is a collection of EJBs. Another possible result is a number of values or fields on certain EJBs that match the query.

A method that can be used in accordance with the system of FIG. 1 is shown in the flowchart of FIG. 2. In the method, a properties object is generated that contains user-specified settings for the query or the finder method, as can be implemented through a user interface of an ejbHome class 200. The appropriate finder method is invoked when the user or application wishes to execute the query 202. The settings are extracted from the properties object and the finder method is parsed in order to generate the appropriate SQL query statement, although other database or data source querying language statements may be generated by the method 204. The SQL query statement is then executed against the database 206.

One embodiment can be implemented through a simple API. To enable the use of dynamic queries, users can add an element to their deployment descriptor, such as:<!ELEMENT enable-dynamic-queries (#PCDATA)>The enable-dynamic-queries element can be a sub-element of a descriptor such as entity-descriptor. The value of enable-dynamic-queries can be either “true” or “false” in this embodiment. Invoking a dynamic query when dynamic queries have not been enabled can result in an exception being thrown, such as java.rmi.AccessException or javax.ejb.AccessLocalException, depending on whether it was invoked from a Remote or Local interface.

A generated implementation class, such as Homelmpl that can be used for all EJB 2.0 Container-Managed Persistence (CMP) beans, can implement a new interface such as QueryHome. A QueryHome interface can declare a single method, such as:

public Object executeQuery(String query, Properties props) throws
       FinderException, RemoteException;

There can also be a local version of QueryHome which may be referred to as QueryLocalHome. The only difference between the interfaces can be the “throws” clause of the executeQuery method. The QueryLocalHome iinterface can declare a single method:

public Object executeQuery(String query, Properties props) throws
       FinderException, EJBException;

The application code can make use of this interface as follows:

InitialContext ic = new InitialContext( );
FooHome fh = (FooHome)ic.lookup(“fooHome”)’
QueryHome qh = (QueryHome)fh;
String query = “SELECT OBJECT(e) FROM EmployeeBean e
WHERE e.name = ‘rob’ “;
Properties props = new Properties( );
props.setProperty(DynamicQuery.MAX_ELEMENTS, “10”);
Collection results = (Collection)qh.executeQuery(query, props);

All options that can currently be specified for a static finder can be set in a Properties object passed to the executeQuery method. The Properties key for all valid options can be defined in a DynamicQuery interface. A list of some valid entries is as follows:

Property:	Value:	Description:
GROUP_NAME	String	The name of the field-group
		whose fields are to be loaded
		into the cache upon execution of
		the query. Note that in order for
		this to work, a finders-load-bean
		or equivalent option may need to
		be enabled for the EJB.
MAX_ELEMENTS	int	The max-elements attribute is
		used to specify the maximum
		number of elements that should
		be returned by a multi-valued
		query. This option can be similar
		to the maxRows feature of
		JDBC.
INCLUDE_UPDATES	boolean	The include-updates tag is used
		to specify that updates made
		during the current transaction
		must be reflected in the result of
		a query.
SQL_SELECT_DISTINCT	boolean	Used to control whether the gen-
		erated SQL ‘SELECT’ will con-
		tain a ‘DISTINCT’ qualifier.
		Use of the DISTINCT qualifier
		will cause the RDBMS to return
		unique rows.
RETURN_TYPE	String	Indicates the return type of the
		executeQuery method. Legal
		values include Collection,
		CursoredCollection, and
		ResultSet. The default value is
		java.util.Collection.
NEW_TRANSACTION	boolean	Indicates whether a new trans-
		action should be started for the
		execution of the DynamicQuery
ISOLATION_LEVEL	String	Indicates the isolation level to be
		used if a new transaction is
		started
RESULT_TYPE_MAPPING	String	Indicates whether EJBObjects or
		EJBLocalObjects should be re-
		turned. The legal values are
		Local and Remote. If the query
		was executed on QueryHome,
		EJBObjects will always be re-
		turned. If the query was exe-
		cuted on QueryLocalHome,
		EJBLocalObjects will be re-
		turned by default. A result-type-
		mapping of Remote can be spe-
		cified in this case if EJBObjects
		are desired.

Ideally, dynamic queries execute nearly as fast as static queries. Dynamic queries can invariably be somewhat slower since the queries can require parsing at runtime, whereas static queries are parsed during deployment. The speed of dynamic queries can be increased, such as by extending them to take query parameters and caching the parsed query String.

The foregoing description of preferred embodiments of the present invention has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Many modifications and variations will be apparent to one of ordinary skill in the relevant arts. The embodiments were chosen and described in order to best explain the principles of the invention and its practical application, thereby enabling others skilled in the art to understand the invention for various embodiments and with various modifications that are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims and their equivalence.

Claims

1. A system for dynamically generating a query to be executed on a database, comprising: a properties object that contains settings for a query as specified by a user, wherein the properties object is generated at runtime and receives the settings from dynamic user input received at runtime;a finder method for initiating the query;a descriptor that contains an enable dynamic queries element, wherein the enable dynamic queries element has a value of either true or false for enabling the query, such that invoking queries when the enable dynamic queries element has a value of false results in a remote or local exception being thrown depending on whether the queries submitted after setting the enable dynamic queries element were invoked from a local interface or a remote interface and wherein the dynamic queries element is specifiable by an enable-dynamic-queries parsed character data (PCDATA) tag, wherein said tag signifies that the dynamic queries element contains character data parsed by an extensible markup language (XML) parser;a server computer that queries the database, the server computer receiving a call from the finder method and reading the settings from the properties object in order to generate the appropriate SQL query statements to be sent to the database, wherein the SQL query statements are generated by parsing the finder method and wherein options that are set for the SQL query statements are specified in the settings contained in the properties object;a database connected to the server computer for executing the dynamically generated SQL query statements; anda collection of results that is returned from the database in response to the finder method, said finder method being invoked on a query home interface used to execute dynamic queries, wherein the collection of results is stored on the server computer.

2. A system according to claim 1, further comprising: a user interface that allows a user to specify the settings in the property object.

3. A system according to claim 1, further comprising: a client containing the properties object and the finder method.

4. A system according to claim 1, further comprising: a bean associated with the database upon which the finder method is invoked.

5. The system of claim 1, wherein the dynamic queries element is a sub-element of said descriptor.

6. The system of claim 1, wherein the settings are used to determine a use of the collection of results that is returned from the database.

7. The system of claim 1, wherein the finder method accepts an instance of a primary key and returns an instance of an entity type.

8. The system of claim 1, wherein the query is programmatically defined and functions slower than a statically defined query for at least one type of application.

9. A system for generating dynamic queries, comprising: a client computer that provides a properties object which contains settings for a query specified by a user, wherein the properties object is generated at runtime and receives the settings from dynamic user input at runtime;a server computer that communicates with the client computer and a database, the server computer providing a bean associated with the database; anda finder method that specifies the query to be executed against the database, the finder method invoked on the bean provided by the server computer;a descriptor that contains an enable dynamic queries element, wherein the enable dynamic queries element has a value of either true or false for enabling the query, such that invoking queries when the enable dynamic queries element has a value of false results in a remote or local exception being thrown depending on whether the queries submitted after setting the enable dynamic queries element were invoked from a local interface or a remote interface, wherein the dynamic queries element is specifiable by an enable-dynamic-queries parsed character data (PCDATA) tag, wherein said tag signifies that the dynamic queries element contains character data parsed by an extensible markup language (XML) parser;wherein upon invocation of the finder method, the server computer extracts the settings contained in the properties object and parses the finder method in order to dynamically generate the query to be sent to the database; anda collection of results that is returned from the database in response to the finder method, said finder method being invoked on a query home interface used to execute dynamic queries.

10. A system according to claim 9 wherein the finder method is declared in a query home interface on the client and server computers.

11. A system according to claim 9, further comprising: a user interface on the client computer for allowing the user to specify the settings contained in the properties object.

12. A system according to claim 9 wherein the bean is an Enterprise Java Bean (EJB) and the size of the EJB deployment descriptor is reduced by dynamically generating the query.

13. A system according to claim 9 wherein the settings specify at least one of: the resulting set of objects returned by the query, the maximum number of elements that should be returned by the query, the return type of the finder method, whether updates made during the current transaction must be reflected in the result of the query and whether a new transaction should be started for the execution of the query.

14. A system according to claim 9 further comprising: a properties key containing entries wherein each entry specifies a setting for the query.