[hibernate-issues] [Hibernate-JIRA] Commented: (HHH-2155) mysql dialect should not generate automatically index for foreign key

[pazkooda (JIRA)]

    [ http://opensource.atlassian.com/projects/hibernate/browse/HHH-2155?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_29990 ] 

pazkooda commented on HHH-2155:
-------------------------------

Citation from "Java Persistence with Hibernate" (Section 8.3.7):
"For example, did you know that indexes on foreign key columns can hurt performance in some situations and therefore aren't automatically
generated by Hibernate? We recommend that DBAs get involved early and verify the automatically generated DDL from Hibernate."

Please take care of this issue. If some one wants such feature it is very easy to apply custom MySql dialect (i.e. she/he can simply copy current one ;) ). Default one should not rather contain automatic index creation.

> mysql dialect should not generate automatically index for foreign key
> ---------------------------------------------------------------------
>
>                 Key: HHH-2155
>                 URL: http://opensource.atlassian.com/projects/hibernate/browse/HHH-2155
>             Project: Hibernate3
>          Issue Type: Improvement
>          Components: core
>         Environment: MySQL
>            Reporter: Anthony Patricio
>            Priority: Minor
>         Attachments: patch-mysqlDialect.txt
>
>
> MySQLDialect.getAddForeignKeyConstraintString(String, String[], String, String[], boolean) method is generating also index which is not wanted.
> Here is the modified method:
> 	public String getAddForeignKeyConstraintString(
> 			String constraintName, 
> 			String[] foreignKey, 
> 			String referencedTable, 
> 			String[] primaryKey, boolean referencesPrimaryKey
> 	) {
> 		String cols = StringHelper.join(", ", foreignKey);
> 		return new StringBuffer(30)
> 			//.append(" add index ")
> 			//.append(constraintName)
> 			//.append(" (")
> 			//.append(cols)
> 			//.append("), add constraint ")
> 			.append(" add constraint ")
> 			.append(constraintName)
> 			.append(" foreign key (")
> 			.append(cols)
> 			.append(") references ")
> 			.append(referencedTable)
> 			.append(" (")
> 			.append( StringHelper.join(", ", primaryKey) )
> 			.append(')')
> 			.toString();
> 	}

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