Patent Publication Number: US-7587417-B2

Title: Systems and methods for dynamic querying

Description:
CLAIM OF PRIORITY 
     This application is a divisional application of U.S. patent application Ser. No. 10/341,107, entitled SYSTEMS AND METHODS FOR DYNAMIC QUERYING, inventors Matthew Shinn, Seth White, and Robert Woollen, filed Jan. 13, 2003, which claims priority to U.S. Provisional Patent Application No. 60/349,432, filed Jan. 18, 2002, entitled ASYSTEMS AND METHODS FOR DYNAMIC QUERYING, both of which are incorporated herein by reference. 
    
    
     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:
 
&lt;!ELEMENT enable-dynamic-queries (#PCDATA)&gt;
 
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.