Keys uniquely identify a record of data which can represent a “case”.
These can be constructed automatically from the answers to questions in the survey. A very simple case is when the key is recognised externally to Smap. For example an identify number. Then the key could be specified as:
Once you have specified a key then you can specify a key policy for your survey.
Survey Key Policy¶
This is the default policy. New records are simply appended even if that creates a duplicate key.
Any submissions that match an existing record using the key will be merged. That is the data in the new record will replace the old record except where the question in the new record was not answered. Then the old data will be retained. For Example.
id: 1 name: Tom age: 20 Address: 5 Smith St.
id: 1 name: Tom age: 21 Address:
id: 1 name: Tom age: 21 Address: 5 Smith St.
The new record will be discarded. This prevents updates to records so should probably not be a common option. It can be used when you want the first record submitted for a key to be the authoratative record.
Similar to discard but this time the original record is replaced by the new one.
Generating a unique key¶
If you don’t have an external unique key that you can use then you can generate one from the data in the record, For example:
Unique keys with a serial number¶
Sometimes there is not enough information in a survey to guarantee a unique key. In this case you can use the serial() function to guarantee that a submission will be unique. For example:
The above serial function will add a unique number to every record starting from 50.
Using serial will make the key policy redundant because every submission will be unique. However these keys can be used as references since they are a unique identifier for a record that can be more human readable than the primary key.
Specifying the key and key policy¶
In the online editor select the menu File then Keys
In the XLSForm editor use the settings sheet.
- THe key goes under the heading key
- The key policy goes under the heading key_policy
A record can be selected to be updated directly either in a task or directly from the console or analysis page. In this case the old record is always replaced. This happens even if the survey has a key and a different key policy such as “merge”.