Class Column

source code

                   object --+                
                            |                
 base.structure.StructureBase --+            
                                |            
                   object --+   |            
                            |   |            
           base.common.Parser --+            
                                |            
base.structure.ParseableStructure --+        
                                    |        
             base.structure.Structure --+    
                                        |    
                           object --+   |    
                                    |   |    
                  base.meta.MetaMixin --+    
                                        |    
                               ColumnBase --+
                                            |
                                           Column

Known Subclasses:

• svcs.outputdef.OutputField

A database column.

Columns contain almost all metadata to describe a column in a database table or a VOTable (the exceptions are for column properties that may span several columns, most notably indices).

Note that the type system adopted by the DC software is a subset of postgres' type system. Thus when defining types, you have to specify basically SQL types. Types for other type systems (like VOTable, XSD, or the software-internal representation in python values) are inferred from them.

Columns can have delimited identifiers as names. Don't do this, it's no end of trouble. For this reason, however, you should not use name but rather key to programmatially obtain field's values from rows.

Properties evaluated:

• std -- set to 1 to tell the tap schema importer to have the column's std column in TAP_SCHEMA 1 (it's 0 otherwise).
• statisticsTarget -- an integer to be set as this column's statistics-gathering target. Set this to something between 100 and 10000 on postgres if you have large tables and columns with strongly non-uniform distributions. Set to -1 to revert to the system default. gavo imp -m will apply changes here.
• targetType -- for a column containing a URL, the media type of the resource pointed at. This is for producing extra annotation for Aladin and friends as per http://mail.ivoa.net/pipermail/dal/2018-May/008017.html

• targetTitle -- if you give targetType, use this to set the link

  title (defaults to "Link").