# ServerLegacyKeyJoin.java

    /*
    ** Module   : ServerLegacyKeyJoin.java
    ** Abstract : Natural join helper implementation for server-side queries,
    **            which uses the "legacy foreign key" fields to perform join.
    **
    ** Copyright (c) 2004-2024, Golden Code Development Corporation.
    **
    ** -#- -I- --Date-- --JPRM-- -----------------------------------Description-----------------------------------
    ** 001 SVL 20080421   @38154 Created initial version. Natural join helper
    **                           for server-side joins using legacy keys.
    ** 002 ECF 20080822   @39563 Added isServerJoin(). Reports whether join
    **                           occurs at database server or within P2J
    **                           runtime environment.
    ** 003 SVL 20140210          Use HQLExpression instead of HQL string.
    ** 004 EVL 20160223          Javadoc fixes to make compatible with Oracle Java 8 for Solaris 10.
    ** 005 ECF 20200906          New ORM implementation.
    **     OM  20221103          New class names for FQLPreprocessor, FQLExpression, FQLBundle, and FQLCache.
    ** 006 OM  20230404          The join navigation key may contain null/unknown values.
    ** 007 OM  20240102          Correctly map the properties of local/inverse buffers.
    */

    /*
    ** This program is free software: you can redistribute it and/or modify
    ** it under the terms of the GNU Affero General Public License as
    ** published by the Free Software Foundation, either version 3 of the
    ** License, or (at your option) any later version.
    **
    ** This program is distributed in the hope that it will be useful,
    ** but WITHOUT ANY WARRANTY; without even the implied warranty of
    ** MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    ** GNU Affero General Public License for more details.
    **
    ** You may find a copy of the GNU Affero GPL version 3 at the following
    ** location: https://www.gnu.org/licenses/agpl-3.0.en.html
    **
    ** Additional terms under GNU Affero GPL version 3 section 7:
    **
    **   Under Section 7 of the GNU Affero GPL version 3, the following additional
    **   terms apply to the works covered under the License.  These additional terms
    **   are non-permissive additional terms allowed under Section 7 of the GNU
    **   Affero GPL version 3 and may not be removed by you.
    **
    **   0. Attribution Requirement.
    **
    **     You must preserve all legal notices or author attributions in the covered
    **     work or Appropriate Legal Notices displayed by works containing the covered
    **     work.  You may not remove from the covered work any author or developer
    **     credit already included within the covered work.
    **
    **   1. No License To Use Trademarks.
    **
    **     This license does not grant any license or rights to use the trademarks
    **     Golden Code, FWD, any Golden Code or FWD logo, or any other trademarks
    **     of Golden Code Development Corporation. You are not authorized to use the
    **     name Golden Code, FWD, or the names of any author or contributor, for
    **     publicity purposes without written authorization.
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    **
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    **
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    **     Golden Code Development Corporation, FWD, or any author or contributor to
    **     the covered work, without written authorization.
    **
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    **
    **     You may not represent the covered work as solely your work.  All modified
    **     versions of the covered work must be marked in a reasonable way to make it
    **     clear that the modified work is not originating from Golden Code Development
    **     Corporation or FWD.  All modified versions must contain the notices of
    **     attribution required in this license.
    */

    package com.goldencode.p2j.persist;

    import java.util.*;
    import com.goldencode.p2j.persist.orm.*;

    /**
     * An implementation of a natural join helper used by query types which
     * perform the join on the database server.  The FQL query string snippet
     * created by this class joins the local DMO with the inverse DMO using the
     * fields which compose the "legacy foreign key" relation, and does not have
     * a query substitution parameter.  For instance, given the three table
     * relationship:
     * <pre>
     *    Person [one-to-many] ---&gt; PersonAddress [many-to-one] ---&gt; Address
     * </pre>
     * and the following multi-table join in Progress
     * <pre>
     *    for each person,
     *        each person-address of person,
     *        each address of person-address:
     *       ...
     * </pre>
     * the first join (<code>person-address of person</code>) is represented as
     * follows:
     * <pre>
     *    personAddress.siteId = person.siteId and
     *    personAddress.empNum = person.empNum
     * </pre>
     * where <code>PersonAddress</code> is the local DMO and Person the foreign
     * DMO;  and the second join (<code>address of person-address</code>) is
     * represented as follows:
     * <pre>
     *    address.addrId = personAddress.addrId
     * </pre>
     * where <code>Address</code> is the local DMO and PersonAddress the foreign
     * DMO.
     */
    final class ServerLegacyKeyJoin
    extends AbstractJoin
    {
       /**
        * Constructor.
        *
        * @param   local
        *          Local record buffer (the refering end of the join).
        * @param   inverse
        *          Inverse record buffer (the referent end of the join).
        */
       ServerLegacyKeyJoin(RecordBuffer local, final RecordBuffer inverse)
       {
          super(local, inverse);
       }

       /**
        * Report whether the join represented by this object takes place at the
        * database server, or within runtime code.
        *
        * @return  <code>true</code> if the join happens at the server;
        *          <code>false</code> if it happens in the runtime.
        */
       protected boolean isServerJoin()
       {
          return true;
       }

       /**
        * Generate the FQL where clause snippet which will be inserted into the overall FQL statement executed by
        * the enclosing query. See the class description for additional details on the composition of the clause.
        *
        * @param   local
        *          Local record buffer (the refering end of the join).
        * @param   inverse
        *          Inverse record buffer (the referent end of the join).
        * @param   info
        *          Relation descriptor object.
        * @param   dereference
        *          {@code true} if the local DMO contains a reference to the foreign record, which must be
        *          dereferenced in the FQL query; {@code false} if the local DMO <i>is</i> the foreign record,
        *          referenced by the inverse DMO.
        *
        * @return  FQL where clause snippets used to perform the join. A bi-dimensional array of clauses are used.
        *          The first dimension is the size of the join (aka the number of fields paired) and the second is
        *          always two: the first (NULL_FIELD) is used when the joined field is {@code null} and the second
        *          (NOT_NULL_FIELD) is used when the join field is not unknown.
        */
       protected FQLExpression[][] generateFQL(RecordBuffer local,
                                               RecordBuffer inverse,
                                               RelationInfo info,
                                               boolean dereference)
       {
          List<FQLExpression> wcListNotNulls = new ArrayList<>();
          List<FQLExpression> wcListNulls = new ArrayList<>();

          boolean switched = local.getDMOImplementationClass() != info.getLocalClass();
          Iterator<String> localProperties = switched ? info.foreignProperties() : info.localProperties();
          Iterator<String> foreignProperties = switched ? info.localProperties() : info.foreignProperties();

          try
          {
             boolean first = true;
             while (localProperties.hasNext() && foreignProperties.hasNext())
             {
                FQLExpression wcNotNull = new FQLExpression();
                FQLExpression wcNull = new FQLExpression();

                if (!first)
                {
                   wcNotNull.append(" and ");
                   wcNull.append(" and ");
                }
                else
                {
                   first = false;
                }

                StringBuilder bufLocal = new StringBuilder();
                DBUtils.composePropertyName(local, localProperties.next(), bufLocal);
                StringBuilder bufForeign = new StringBuilder();
                DBUtils.composePropertyName(inverse, foreignProperties.next(), bufForeign);

                wcNotNull.append(bufLocal.toString()).append(" = ").append(bufForeign.toString());
                wcNull.append(bufLocal.toString()).append(" is null");

                wcListNotNulls.add(wcNotNull);
                wcListNulls.add(wcNull);
             }
          }
          catch (PersistenceException e)
          {
             // RelationInfo contains incorrect information
             throw new IllegalArgumentException(e);
          }

          // collect result and construct the 2-dimensional return array
          int len = wcListNotNulls.size();
          FQLExpression[][] ret = new FQLExpression[len][2];
          for (int i = 0; i < len; i++)
          {
             ret[i][NULL_FIELD] = wcListNulls.get(i);
             ret[i][NOT_NULL_FIELD] = wcListNotNulls.get(i);
          }
          return ret;
       }

       /**
        * Get the values of DMO instance fields which will be used as the query substitution
        * parameters. Since this implementation utilizes no query substitution parameters, this method
        * always returns {@code null}.
        *
        * @param   info
        *          Not used.
        * @param   dereference
        *          Not used.
        *
        * @return  {@code null}.
        */
       @Override
       protected List<FqlType> getParameterTypes(RelationInfo info, boolean dereference)
       {
          return null;
       }
    }