source: trunk/src/groovy/HqlBuilder.groovy @ 641

/* Copyright 2010 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

/**
 * Provides a DSL for building and managing HQL strings.
 * For usage examples see the HqlBuilderTests.
 * HQL reference see http://docs.jboss.org/hibernate/core/3.6/reference/en-US/html/queryhql.html
 *
 * Primary goals:
 * 1. Easy to read and understand in code.
 * 2. Easy to read and understand when printed (e.g when displayed in a report).
 * 3. Easy to execute with correct paginateParams and namedParams.
 * 4. Easy to change a clause and execute again.
 *
 * @author Gavin Kromhout
 * @version DraftA
 *
 */
class HqlBuilder {

    // Query clauses.
    // Each clause is a key with a list of terms.
    def clauses = [:]

    // HQL namedParams.
    // HQL requires the namedParams to match exactly with the clause expressions.
    def namedParams = [:]

    // HQL paginateParams.
    def paginateParams = [max: 1000, offset: 0]

    // It is easier and more flexible to simply add order as a clause, e.g: order 'by id asc'
    //def sort = "" // e.g. instanceName.id
    //def order = "" // e.g. asc or desc

    def HqlBuilder(debug = false) {
        if(!super.metaClass.hasMetaProperty('log'))
            mockLogging(debug)
        log.debug "HqlBuilder()"
    }

    def call() {
        log.debug "call()"
    }

    /**
     * Call with closure as last arg.
     * A typically used build call, e.g: q { } is equivalent to q.call() { }
     */
    def call(Closure cl) {
        log.debug "call(Closure cl)"
        handleClosure(cl)
    }

    /**
     * Domain specific build method.
     *  Has no real use other than to prevent obscure errors
     * when user makes a call to query() and Groovy calls query(Closure cl)
     * @returns This object.
     */
    def query() {
        log.debug "query()"
        return this // Must return this object to q.
    }

    /**
     * Domain specific build method.
     * A typically used build call, e.g: def q = new HqlBuilder().query { }
     *
     * @param cl The supplied Closure.
     * @returns This object.
     *
     */
    def query(Closure cl) {
        log.debug "query(Closure cl)"
        handleClosure(cl)
        return this // Must return this object to q.
    }

    /**
     * InvokeMethod resolves all undefined methods.
     * Which include the clause methods, e.g select 'book' is equivalent to select('book').
     * Note that defined methods will be called directly since this class does not implement GroovyInterceptable.
     * If class was "HqlBuilder implements GroovyInterceptable" then even println would be intercepted and
     * several exlusions might be needed. e.g: if(methodName != 'call' && methodName != 'println')
     */
    def invokeMethod(String name, args) {

        log.debug "invokeMethod(${methodName}, ${args})"

        if(!this.clauses[name])
            this.clauses[name] = []

        for(arg in args) {
            if(arg instanceof String)
                this.clauses[name] << arg
        }

        if(args[-1] instanceof Closure)
            handleClosure(args[-1])

    } // invokeMethod()

    /**
     * PropertyMissing.
     * Allows clauses to be added after build, e.g: q.order = 'by book.name asc'
     * and clauses to be removed, e.g: q.order = null
     */
    def propertyMissing(String name, value) {
        log.debug "propertyMissing(${propertyName}, ${value})"
        if(value == null) {
            clauses.remove(name)
            return
        }

        if(value instanceof String)
            clauses[name] = [value]
    }

    /**
     * PropertyMissing.
     * Allow clauses to be accessed directly by name, e.g: println q.order.
     * Since clauses is a Map null is simply returned for a non-existant clause.
     */
    def propertyMissing(String name) {
        log.debug "propertyMissing(${name})"
        clauses[name]
    }

    /**
     * HandleClosure.
     * Setting delegate and DELEGATE_FIRST allows closure to access this object's properties first.
     */
    private handleClosure(Closure cl) {
        cl.delegate = this
        cl.resolveStrategy = Closure.DELEGATE_FIRST
        cl.call()
    }

    /**
     * MockLogging.
     * This class has super cow powers and can mock out it's own debug logging.
     */
    private mockLogging(debug = false) {
        def mockLogger = {}
        if(debug) {
            mockLogger = {msg ->
                    println "${super.getClass()} - DEBUG: $msg"
            }
        }
        super.metaClass.log = [debug: mockLogger]
        log.debug "Internal mockLogger configured."
    }

    /**
     * GetQuery.
     * Assemble and return the query in a format that can be directly executed.
     * E.g: executeQuery(q.query, q.namedParams, q.paginateParams).
     */
    def getQuery() {
        this.clauses.collect {
            it.key + ' ' + it.value.join(' ')
        }.join(' ')
    }

    /**
     * GetPrintFormattedQuery.
     * Assemble and return the query in a format that can be more easily printed and read by a person.
     * E.g: println q.printFormattedQuery or when displayed in a report.
     */
    def getPrintFormattedQuery() {
        this.clauses.collect {
            it.key + ' ' + it.value.join(' \n')
        }.join(' \n')
    }

} // end class