Kexi/Plugins/Tables/Simple alter table

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Design page for task: "Add support for alter table's design without losing data".

Contents

Rationale

Approach when modification to table schema is saved directly after user performed it is much easier than full alter table tried in Kexi 1.x and never delivered.

Analysis

  • Altering some physical properties would require immediate saving of the design but will not remove all the data.
  • Other properties (for which KexiDB::isExtendedTableFieldProperty() return true) can be modified without altering any data.

Alter actions

This section publishes details on particular actions of table altering.

Caption rename

  • status: TODO
  • unit testing: TODO
  • triggers name change in property editor, so:
    • A: if name changed, ask for accepting name change:
      • if accepted go to #Name change section
      • if not accepted, revert the recent name change and go to B
    • B: else, do nothing, caption should be saved on Save action

Name change

  • status: TODO
  • unit testing: TODO
  • can happen after:
    • change of caption (see Caption rename)
    • or name value changes in the property editor
  • request instant applying
  • Algorithm:
    • if name is duplicated, display info and abort
    • ALTER TABLE available: send to the backend
    • ALTER TABLE not available:
      • Create full table copy with all fields but with one field renamed
      • Copy all records to the new table
      • Drop the original table
      • Rename table to the original name
      • Update table metadata
  • Notes:
    • tables that reference to the renamed field via relationships may need updates
    • queries that reference to the renamed field may need updates

Field removing

  • status: TODO
  • unit testing: TODO
  • triggered by "Delete Record" action, available in context menu
  • request instant applying
  • Algorithm:
    • ALTER TABLE available: send to the backend
    • ALTER TABLE not available:
      • Create full table copy with all fields but the one fields removed
      • Copy all records to the new table
      • Drop the original table
      • Rename table to the original name
    • Update table metadata
  • Notes:
    • tables that reference to the renamed field via relationships may need updates
    • queries that reference to the renamed field may need updates

Fields reordering

  • status: TODO
  • unit testing: TODO
  • triggered after accepting "Reorder Fields" dialog
  • request instant applying
  • Algorithm:
    • ALTER TABLE available: send to the backend
    • ALTER TABLE not available:
      • Create full table copy with all fields in destination order
      • Copy all records to the new table with new order
      • Drop the original table
      • Rename table to the original name
    • Update table metadata
  • Notes:
    • queries that use "ORDER by <number>" clause will have to be updated

Field inserting

  • status: TODO
  • unit testing: TODO
  • triggered after inserting new field's definition into empty row anywhere at 0..N position
  • Algorithm:
    • ALTER TABLE available: send to the backend
    • ALTER TABLE available for appending field (e.g. SQLite), and the new field should be appended:
      • send use respective ALTER TABLE command
    • ALTER TABLE not available:
      • Create full table copy with all fields plus one new field
      • Copy all records to the new table with new specified order
      • Drop the original table
      • Rename table to the original name
    • Update table metadata
  • Notes:
    • queries that already use name that has been added may need updates

Field type change

Byte Field type change

  • status: TODO
  • unit testing: TODO
  • To Byte - N/A
  • To ShortInteger
  • To Integer
  • To BigInteger
  • To Boolean
  • To Date
  • To DateTime
  • To Time
  • To Float
  • To Double
  • To Text
  • To LongText
  • To BLOB

ShortInteger Field type change

  • status: TODO
  • unit testing: TODO
  • To Byte
  • To ShortInteger - N/A
  • To Integer
  • To BigInteger
  • To Boolean
  • To Date
  • To DateTime
  • To Time
  • To Float
  • To Double
  • To Text
  • To LongText
  • To BLOB

Integer Field type change

  • status: TODO
  • unit testing: TODO
  • To Byte
  • To ShortInteger
  • To Integer - N/A
  • To BigInteger
  • To Boolean
  • To Date
  • To DateTime
  • To Time
  • To Float
  • To Double
  • To Text
  • To LongText
  • To BLOB

BigInteger Field type change

  • status: TODO
  • unit testing: TODO
  • To Byte
  • To ShortInteger
  • To Integer
  • To BigInteger - N/A
  • To Boolean
  • To Date
  • To DateTime
  • To Time
  • To Float
  • To Double
  • To Text
  • To LongText
  • To BLOB

Boolean type change

  • status: TODO
  • unit testing: TODO
  • To Byte
  • To ShortInteger
  • To Integer
  • To BigInteger
  • To Boolean - N/A
  • To Date
  • To DateTime
  • To Time
  • To Float
  • To Double
  • To Text
  • To LongText
  • To BLOB

Date type change

  • status: TODO
  • unit testing: TODO
  • To Byte
  • To ShortInteger
  • To Integer
  • To BigInteger
  • To Boolean
  • To Date - N/A
  • To DateTime
  • To Time
  • To Float
  • To Double
  • To Text
  • To LongText
  • To BLOB

DateTime type change

  • status: TODO
  • unit testing: TODO
  • To Byte
  • To ShortInteger
  • To Integer
  • To BigInteger
  • To Boolean
  • To Date
  • To DateTime - N/A
  • To Time
  • To Float
  • To Double
  • To Text
  • To LongText
  • To BLOB

Time type change

  • status: TODO
  • unit testing: TODO
  • To Byte
  • To ShortInteger
  • To Integer
  • To BigInteger
  • To Boolean
  • To Date
  • To DateTime
  • To Time - N/A
  • To Float
  • To Double
  • To Text
  • To LongText
  • To BLOB

Float type change

  • status: TODO
  • unit testing: TODO
  • To Byte
  • To ShortInteger
  • To Integer
  • To BigInteger
  • To Boolean
  • To Date
  • To DateTime
  • To Time
  • To Float - N/A
  • To Double
  • To Text
  • To LongText
  • To BLOB

Double type change

  • status: TODO
  • unit testing: TODO
  • To Byte
  • To ShortInteger
  • To Integer
  • To BigInteger
  • To Boolean
  • To Date
  • To DateTime
  • To Time
  • To Float
  • To Double - N/A
  • To Text
  • To LongText
  • To BLOB

Text type change

  • status: TODO
  • unit testing: TODO
  • To Byte
  • To ShortInteger
  • To Integer
  • To BigInteger
  • To Boolean
  • To Date
  • To DateTime
  • To Time
  • To Float
  • To Double
  • To Text - N/A
  • To LongText
  • To BLOB

LongText type change

  • status: TODO
  • unit testing: TODO
  • To Byte
  • To ShortInteger
  • To Integer
  • To BigInteger
  • To Boolean
  • To Date
  • To DateTime
  • To Time
  • To Float
  • To Double
  • To Text
  • To LongText - N/A
  • To BLOB

BLOB type change

  • status: TODO
  • unit testing: TODO
  • To Byte
  • To ShortInteger
  • To Integer
  • To BigInteger
  • To Boolean
  • To Date
  • To DateTime
  • To Time
  • To Float
  • To Double
  • To Text
  • To LongText
  • To BLOB - N/A

Lookup fields change

Lookup fields are defined by extended schema's properties: rowSourceType, rowSource, boundColumn, visibleColumn, rowSourceValues.

Altering requirements: ExtendedSchemaAlteringRequired

  • status: DONE
  • unit testing:
    • adding DONE
    • removing TODO
    • altering TODO

Requirements

  • Full data safety
    • It's better to warn and request data removal than claiming it is not necessary and then doing that
    • Enclose operations within transactions
  • Altering requirement should depends on type of connection/driver. For example, MySQL has built-in ALTER TABLE while SQLite almost completely lacks it.
   //! Defines flags for possible altering requirements; can be combined.
   enum AlteringRequirements {
       /*! Physical table altering is required; e.g. ALTER TABLE ADD COLUMN. */
       PhysicalAlteringRequired = 1,

       /*! Data conversion is required; e.g. converting integer
        values to string after changing column type from integer to text. */
       DataConversionRequired = 2,

       /*! Changes to the main table schema (in kexi__fields) required,
        this does not require physical changes for the table;
        e.g. changing value of the "caption" or "description" property. */
       MainSchemaAlteringRequired = 4,

       /*! Only changes to extended table schema required,
        this does not require physical changes for the table;
        e.g. changing value of the "visibleDecimalPlaces" property
        or any of the custom properties. */
       ExtendedSchemaAlteringRequired = 8,

       /*! Convenience flag, changes to the main or extended schema is required. */
       SchemaAlteringRequired = ExtendedSchemaAlteringRequired | MainSchemaAlteringRequired
   };

Hints

  • Table rename in SQLite: ALTER TABLE RENAME TO...
  • Full table copy in SQLite: CREATE TABLE copy AS SELECT * FROM t;

Links


This page was last modified on 6 February 2014, at 00:59. This page has been accessed 1,156 times. Content is available under Creative Commons License SA 3.0 as well as the GNU Free Documentation License 1.2.
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