Kexi/Plugins/Tables/Simple alter table

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< Kexi‎ | Plugins‎ | Tables

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

Rationale

Approach when modification to table schema is saved directly after user performed it is much easier than full alter table tired 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
  • 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
  • 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
  • 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
  • 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
  • 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
  • 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
  • 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
  • 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
  • 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
  • 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
  • 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
  • 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
  • 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
  • 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
  • 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
  • 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
  • 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
  • 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

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;

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