| 1 | /* |
| 2 | |
| 3 | Derby - Class org.apache.derby.impl.store.access.sort.SortScan |
| 4 | |
| 5 | Copyright 1997, 2004 The Apache Software Foundation or its licensors, as applicable. |
| 6 | |
| 7 | Licensed under the Apache License, Version 2.0 (the "License"); |
| 8 | you may not use this file except in compliance with the License. |
| 9 | You may obtain a copy of the License at |
| 10 | |
| 11 | http://www.apache.org/licenses/LICENSE-2.0 |
| 12 | |
| 13 | Unless required by applicable law or agreed to in writing, software |
| 14 | distributed under the License is distributed on an "AS IS" BASIS, |
| 15 | WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| 16 | See the License for the specific language governing permissions and |
| 17 | limitations under the License. |
| 18 | |
| 19 | */ |
| 20 | |
| 21 | package org.apache.derby.impl.store.access.sort; |
| 22 | |
| 23 | import org.apache.derby.iapi.reference.SQLState; |
| 24 | |
| 25 | import org.apache.derby.iapi.services.io.FormatableBitSet; |
| 26 | |
| 27 | import org.apache.derby.iapi.services.sanity.SanityManager; |
| 28 | import org.apache.derby.iapi.services.io.Storable; |
| 29 | |
| 30 | import org.apache.derby.iapi.error.StandardException; |
| 31 | |
| 32 | import org.apache.derby.iapi.store.access.conglomerate.TransactionManager; |
| 33 | import org.apache.derby.iapi.store.access.RowUtil; |
| 34 | import org.apache.derby.iapi.store.access.ScanController; |
| 35 | |
| 36 | import org.apache.derby.iapi.types.DataValueDescriptor; |
| 37 | |
| 38 | |
| 39 | /** |
| 40 | |
| 41 | Abstract base class for merge sort scans. |
| 42 | |
| 43 | **/ |
| 44 | |
| 45 | public abstract class SortScan extends Scan |
| 46 | { |
| 47 | |
| 48 | /** |
| 49 | The sort that this class is scanning. |
| 50 | **/ |
| 51 | protected MergeSort sort = null; |
| 52 | |
| 53 | /** |
| 54 | The transactionManager that opened this scan. |
| 55 | **/ |
| 56 | protected TransactionManager tran = null; |
| 57 | |
| 58 | /** |
| 59 | The row at the current position of the scan, from which |
| 60 | fetch will return values. |
| 61 | **/ |
| 62 | protected DataValueDescriptor[] current; |
| 63 | |
| 64 | /** |
| 65 | The row at the current position of the scan, from which |
| 66 | fetch will return values. |
| 67 | **/ |
| 68 | protected boolean hold; |
| 69 | |
| 70 | /* |
| 71 | * Constructors |
| 72 | */ |
| 73 | SortScan(MergeSort sort, TransactionManager tran, boolean hold) |
| 74 | { |
| 75 | super(); |
| 76 | this.sort = sort; |
| 77 | this.tran = tran; |
| 78 | this.hold = hold; |
| 79 | } |
| 80 | |
| 81 | /* |
| 82 | * Abstract methods of Scan |
| 83 | */ |
| 84 | |
| 85 | /** |
| 86 | Fetch the row at the next position of the Scan. |
| 87 | |
| 88 | If there is a valid next position in the scan then |
| 89 | the value in the template storable row is replaced |
| 90 | with the value of the row at the current scan |
| 91 | position. The columns of the template row must |
| 92 | be of the same type as the actual columns in the |
| 93 | underlying conglomerate. |
| 94 | |
| 95 | The resulting contents of templateRow after a fetchNext() |
| 96 | which returns false is undefined. |
| 97 | |
| 98 | The result of calling fetchNext(row) is exactly logically |
| 99 | equivalent to making a next() call followed by a fetch(row) |
| 100 | call. This interface allows implementations to optimize |
| 101 | the 2 calls if possible. |
| 102 | |
| 103 | RESOLVE (mikem - 2/24/98) - come back to this and see if |
| 104 | coding this differently saves in sort scans, as did the |
| 105 | heap recoding. |
| 106 | |
| 107 | @param row The template row into which the value |
| 108 | of the next position in the scan is to be stored. |
| 109 | |
| 110 | @return True if there is a next position in the scan, |
| 111 | false if there isn't. |
| 112 | |
| 113 | @exception StandardException Standard exception policy. |
| 114 | **/ |
| 115 | public final boolean fetchNext(DataValueDescriptor[] row) |
| 116 | throws StandardException |
| 117 | { |
| 118 | boolean ret_val = next(); |
| 119 | |
| 120 | if (ret_val) |
| 121 | fetch(row); |
| 122 | |
| 123 | return(ret_val); |
| 124 | } |
| 125 | |
| 126 | /** |
| 127 | Fetch the row at the current position of the Scan. |
| 128 | @see ScanController#fetch |
| 129 | **/ |
| 130 | public final void fetch(DataValueDescriptor[] result) |
| 131 | throws StandardException |
| 132 | { |
| 133 | if (SanityManager.DEBUG) |
| 134 | { |
| 135 | SanityManager.ASSERT(sort != null); |
| 136 | } |
| 137 | |
| 138 | if (current == null) |
| 139 | { |
| 140 | throw StandardException.newException( |
| 141 | SQLState.SORT_SCAN_NOT_POSITIONED); |
| 142 | } |
| 143 | |
| 144 | // Make sure the passed in template row is of the correct type. |
| 145 | sort.checkColumnTypes(result); |
| 146 | |
| 147 | // RESOLVE |
| 148 | // Note that fetch() basically throws away the object's passed in. |
| 149 | // We should figure out how to allow callers in this situation to |
| 150 | // not go through the work of allocating objects in the first place. |
| 151 | |
| 152 | // Sort has allocated objects for this row, and will not |
| 153 | // reference them any more. So just pass the objects out |
| 154 | // to the caller instead of copying them into the provided |
| 155 | // objects. |
| 156 | System.arraycopy(current, 0, result, 0, result.length); |
| 157 | } |
| 158 | |
| 159 | /** |
| 160 | Fetch the row at the current position of the Scan and does not apply the |
| 161 | qualifiers. |
| 162 | |
| 163 | This method will always throw an exception. |
| 164 | (SQLState.SORT_IMPROPER_SCAN_METHOD) |
| 165 | |
| 166 | @see ScanController#fetchWithoutQualify |
| 167 | **/ |
| 168 | public final void fetchWithoutQualify(DataValueDescriptor[] result) |
| 169 | throws StandardException |
| 170 | { |
| 171 | throw StandardException.newException( |
| 172 | SQLState.SORT_IMPROPER_SCAN_METHOD); |
| 173 | |
| 174 | } |
| 175 | |
| 176 | /** |
| 177 | Close the scan. @see ScanController#close |
| 178 | **/ |
| 179 | public void close() |
| 180 | { |
| 181 | sort = null; |
| 182 | current = null; |
| 183 | |
| 184 | tran.closeMe(this); |
| 185 | } |
| 186 | |
| 187 | /* |
| 188 | * Methods of SortScan. Arranged alphabetically. |
| 189 | */ |
| 190 | } |