Hibernate ORM - hibernate-core 6.4.4.Final · org.hibernate.dialect.unique.UniqueDelegate

Dialect-level delegate responsible for applying unique constraints in DDL. Uniqueness can be specified in any of three ways:

For single-column constraints, by adding unique to the column definition. See getColumnDefinitionUniquenessFragment
By inclusion of the unique constraint in the create table statement. See getTableCreationUniqueConstraintsFragment
By creation of a unique constraint using separate alter table statements. See getAlterTableToAddUniqueKeyCommand. Also, see getAlterTableToDropUniqueKeyCommand.

The first two options are generally preferred, and so we use CreateTableUniqueDelegate where possible. However, for databases where unique constraints may not contain a nullable column, and unique indexes must be used instead, we use AlterTableUniqueIndexDelegate.

Hibernate specifies that a unique constraint on a nullable column considers null values to be distinct. Some databases default to the opposite semantic, where null values are considered equal for the purpose of determining uniqueness. This is almost never useful, and is the opposite of what we want when we use a unique constraint on a foreign key to map an optional org.hibernate.mapping.OneToOne association. Therefore, our UniqueDelegates must jump through hoops to emulate the sensible semantics specified by ANSI, Hibernate, and common sense, namely, that two null values are distinct. A particularly egregious offender is Sybase, where we must simply skip creating the unique constraint.

Method Summary

Modifier and Type	Method and Description
public String	Returns: The `alter table` command getAlterTableToAddUniqueKeyCommand(UniqueKey The `UniqueKey` instance. Contains all information about the columns uniqueKey, Metadata Access to the bootstrap mapping information metadata, SqlStringGenerationContext A context for SQL string generation context) Deprecated as a consequence of `Metadata` being deprecated. Get the `alter table` command used to create the given unique key constraint, or return the empty string if the constraint was already included in the `create table` statement by `getTableCreationUniqueConstraintsFragment`.
public String	Returns: The `alter table` command getAlterTableToDropUniqueKeyCommand(UniqueKey The `UniqueKey` instance. Contains all information about the columns uniqueKey, Metadata Access to the bootstrap mapping information metadata, SqlStringGenerationContext A context for SQL string generation context) Deprecated as a consequence of `Metadata` being deprecated. Get the `alter table` command used to drop the given unique key which was previously created by `getAlterTableToAddUniqueKeyCommand`.
public String	Returns: The fragment (usually "unique"), empty string indicates the uniqueness will be indicated using a different approach getColumnDefinitionUniquenessFragment(Column The column to which to apply the unique column, SqlStringGenerationContext A context for SQL string generation context) Get the SQL fragment used to make the given column unique as part of its column definition, usually just `" unique"`, or return an empty string if uniqueness does not belong in the column definition.
public String	Returns: The fragment, typically in the form `", unique(col1, col2), unique(col20)"`. The leading comma is important! getTableCreationUniqueConstraintsFragment(Table The table for which to generate the unique constraints fragment table, SqlStringGenerationContext A context for SQL string generation context) Get the SQL fragment used to specify the unique constraints on the given table as part of the `create table` command, with a leading comma, usually something like: `, unique(x,y), constraint abc unique(a,b,c)`

Method Detail

getAlterTableToAddUniqueKeyCommand back to summary

public String getAlterTableToAddUniqueKeyCommand(UniqueKey uniqueKey, Metadata metadata, SqlStringGenerationContext context)

Deprecated

as a consequence of Metadata being deprecated. See corresponding docs for further information.

Get the alter table command used to create the given unique key constraint, or return the empty string if the constraint was already included in the create table statement by getTableCreationUniqueConstraintsFragment.

Parameters

uniqueKey:UniqueKey: The UniqueKey instance. Contains all information about the columns
metadata:Metadata: Access to the bootstrap mapping information
context:SqlStringGenerationContext: A context for SQL string generation

Returns:String

The alter table command

getAlterTableToDropUniqueKeyCommand back to summary

public String getAlterTableToDropUniqueKeyCommand(UniqueKey uniqueKey, Metadata metadata, SqlStringGenerationContext context)

Deprecated

as a consequence of Metadata being deprecated. See corresponding docs for further information.

Get the alter table command used to drop the given unique key which was previously created by getAlterTableToAddUniqueKeyCommand.

Parameters

uniqueKey:UniqueKey: The UniqueKey instance. Contains all information about the columns
metadata:Metadata: Access to the bootstrap mapping information
context:SqlStringGenerationContext: A context for SQL string generation

Returns:String

The alter table command

getColumnDefinitionUniquenessFragment back to summary

getColumnDefinitionUniquenessFragment	back to summary
public String getColumnDefinitionUniquenessFragment(Column column, SqlStringGenerationContext context) Get the SQL fragment used to make the given column unique as part of its column definition, usually just `" unique"`, or return an empty string if uniqueness does not belong in the column definition. This is for handling single columns explicitly marked unique, not for dealing with unique keys. Parameters column:Column The column to which to apply the unique context:SqlStringGenerationContext A context for SQL string generation Returns:String The fragment (usually "unique"), empty string indicates the uniqueness will be indicated using a different approach

public String getColumnDefinitionUniquenessFragment(Column column, SqlStringGenerationContext context)

Get the SQL fragment used to make the given column unique as part of its column definition, usually just " unique", or return an empty string if uniqueness does not belong in the column definition.

This is for handling single columns explicitly marked unique, not for dealing with unique keys.

Parameters

column:Column: The column to which to apply the unique
context:SqlStringGenerationContext: A context for SQL string generation

Returns:String

The fragment (usually "unique"), empty string indicates the uniqueness will be indicated using a different approach

getTableCreationUniqueConstraintsFragment back to summary

getTableCreationUniqueConstraintsFragment	back to summary
public String getTableCreationUniqueConstraintsFragment(Table table, SqlStringGenerationContext context) Get the SQL fragment used to specify the unique constraints on the given table as part of the `create table` command, with a leading comma, usually something like: `, unique(x,y), constraint abc unique(a,b,c)` or return an empty string if there are no unique constraints or if the unique constraints do not belong in the table definition. The implementation should iterate over the unique keys of the given table by calling `org.hibernate.mapping.Table#getUniqueKeys()` and generate a fragment which includes all the unique key declarations. Parameters table:Table The table for which to generate the unique constraints fragment context:SqlStringGenerationContext A context for SQL string generation Returns:String The fragment, typically in the form `", unique(col1, col2), unique(col20)"`. The leading comma is important!

public String getTableCreationUniqueConstraintsFragment(Table table, SqlStringGenerationContext context)

Get the SQL fragment used to specify the unique constraints on the given table as part of the create table command, with a leading comma, usually something like:

, unique(x,y), constraint abc unique(a,b,c)

or return an empty string if there are no unique constraints or if the unique constraints do not belong in the table definition.

The implementation should iterate over the unique keys of the given table by calling org.hibernate.mapping.Table#getUniqueKeys() and generate a fragment which includes all the unique key declarations.

Parameters

table:Table: The table for which to generate the unique constraints fragment
context:SqlStringGenerationContext: A context for SQL string generation

Returns:String

The fragment, typically in the form ", unique(col1, col2), unique(col20)". The leading comma is important!

public Interface UniqueDelegate

Method Summary

Method Detail