| **Navigation:**  [[introduction.htm|Language Reference]] > [[chapter runtime properties.htm|App C - PROP: Runtime Properties]] > Runtime VIEW and FILE Properties >====== PROP:DuplicateKey ====== | [[prop driverlogsoutalias.htm|{{btn_prev_n.gif|Previous page}}]][[chapter runtime properties.htm|{{btn_home_n.gif|Return to chapter overview}}]][[prop fetchsize.htm|{{btn_next_n.gif|Next page}}]] |
|  ||

Read-Only property of a FILE that returns the key that caused the last duplicate key error. It is cleared only when a subsequent ADD or PUT is attempted.

It is very common that you want to know which key causes a duplicate key error after you do a PUT or an ADD. At present you do this by looping through all keys that a file has and testing for DUPLICATE for each key until you find one. This is inefficient and requires a fair amount of code. Generally, the file drivers already know which key you are looking for, so why not ask the driver for the key. You can now do this using PROP:DuplicateKey.

**Example:**

| **  PROGRAM** |
|  |
| **  MAP** |
| **  END** |
|  |
| **f FILE,DRIVER('Clarion'),CREATE,PRE(f)** |
| **pk KEY(f:fld1)** |
| **   RECORD** |
| **fld1 LONG** |
| **   END** |
| **  END** |
|  |
| **k &KEY** |
| **  CODE** |
| **   CREATE(f)** |
| **   OPEN(f)** |
| **   f.fld1 = 1** |
| **   ADD(f)** |
| **   f.fld1 = 2** |
| **   ADD(f)** |
| **   k &= f{PROP:DuplicateKey} ! k is NULL at this stage because no duplicate has occurred** |
| **   f.fld1 = 1** |
| **   PUT(f)** |
| **   k &= f{PROP:DuplicateKey} ! k will be set to f:pk as the PUT caused a ** |
| **                             ! duplicate key error** |
| **   SET(pk)** |
| **   GET(pk)** |
| **   f.fld1 = 7** |
| **   k &= f{PROP:DuplicateKey} ! k will be still be set at this stage** |
| **   PUT(f)** |
| **   k &= f{PROP:DuplicateKey} ! k will be NULL now** |