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Bret McGuire commented on CASSANDRA-20003:
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There is some definite subtlety here.
SchemaBuilder.alterTable() returns AlterTableStart which extends several
operation-specific interfaces (AlterTableAddColumn, AlterTableDropColumn, etc).
Methods on each of these return a corresponding *End interface
(AlterTableDropColumn.dropColum() and variants returns AlterTableDropColumnEnd
for instance) and these *End interfaces extend their corresponding basic
interface (AlterTableDropColumnEnd extends AlterTableDropColumn). This allows
for nice iterative creation of DDL statements via multiple method calls on the
builder.
Thing is... the PR added support for "if exists" and "if not exists" at the
table _and_ at the column level. Examples provided in CASSANDRA-16916 make
that clear:
* {{ALTER TABLE IF EXISTS myTable ...}}
* {{ALTER TABLE myTable ADD IF NOT EXISTS ...}}
* {{ALTER TABLE myTable DROP IF EXISTS ...}}
* {{ALTER TYPE IF EXISTS myType ...}}
* {{ALTER TYPE myType ADD IF NOT EXISTS ...}}
In an ideal world we'd prolly just add "ifExists()" to both
AlterTableDropColumn and AlterTableDropColumnEnd. But since _all_ of these
interfaces are implemented by a single object (DefaultAlterTable) we have no
idea of knowing whether the ifExists() method in DefaultAlterTable is being
called from the table or column builder.
Prolly easiest to just use ifTableExists() and ifColumnExists(). It's slightly
more verbose but it maintains all the current abstractions.
> Add query builder support for "IF EXISTS" and "IF NOT EXISTS" in alter
> statements
> ---------------------------------------------------------------------------------
>
> Key: CASSANDRA-20003
> URL: https://issues.apache.org/jira/browse/CASSANDRA-20003
> Project: Cassandra
> Issue Type: Improvement
> Components: Client/java-driver
> Reporter: Bret McGuire
> Assignee: Bret McGuire
> Priority: Normal
>
> CASSANDRA-16916 added support for IF EXISTS and IF NOT EXISTS in alter
> statements. The fix version indicates that this change was aimed at the
> 4.1.x release. The driver's query builder should support this syntax as well.
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