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From Rick Hillegas <Richard.Hille...@Sun.COM>
Subject Re: how to get names of column constraints ?
Date Fri, 09 May 2008 17:23:14 GMT
Hi Maris,

When you declare a constraint, Derby creates a backing index for that 
constraint. If you do not explicitly name the constraint, then Derby 
will make up a name. The constraint name which Derby makes up is the 
same name that Derby gives to the backing index. If you don't name your 
constraints, then you can use DatabaseMetaData.getIndexInfo() to find 
the system-generated constraint names. However, if you do name your 
constraints (as you did below with a unique constraint named 
RECEIPT_REC_REF), then the backing index name will not match the 
constraint name. For primary key constraints, you can use 
DatabaseMetaData.getPrimaryKeys() to find the correct name for primary 
keys (either user supplied or system generated). I don't see parallel 
DatabaseMetaData methods for unique and foreign key constraints.

I am attaching two files which demonstrate this behavior:

DBMetaData.java - This is a compact set of VTIs which present some 
DatabaseMetaData methods as table functions.

dbmetadata.sql - This script declares the table functions and uses them 
to present getIndexInfo() and getPrimaryKey() information alongside 
queries against the Derby catalogs.

Hope this helps,
-Rick


Maris Orbidans wrote:
> Yes, please run attached class.
>
> Using metadata it finds those two indexes and fails to drop last one.
>
> Table: RECEIPT Index: SQL080509095407610
> Table: RECEIPT Index: SQL080509095407630
> java.sql.SQLSyntaxErrorException: ALTER TABLE failed. There is no
> constraint 'APP.SQL080509095407630' on table '"APP"."RECEIPT"'.
>
> If you use method dropUsingSysconstraints(con) instead dropUsingMetadata
> then everything works.
>
> SQL080509095407610
> RECEIPT_REC_REF
>
> Maris
>
> -----Original Message-----
> From: Dag.Wanvik@Sun.COM [mailto:Dag.Wanvik@Sun.COM] 
> Sent: 08 May 2008 14:32
> To: Derby Discussion
> Subject: Re: how to get names of column constraints ?
>
> Maris Orbidans <maris.orbidans@ingg.com> writes:
>
>   
>> I know I can read constraint names from SYS.SYSCONSTRAINTS but can I
>>     
> get
>   
>> it from DatabaseMetaData?  
>>
>> I am trying to get ha-jdbc synchronization working with my derby
>> database. The problem is that ha-jdbc reads INDEX_NAMEs from
>> DatabaseMetaData  (with getIndexInfo) and assumes that column
>>     
> constraint
>   
>> has the same name and tries to drop it. 
>>     
>
> Not sure what your exact problem is, can you post a standalone repro?
> I tried the following which worked:
>
>    st.execute("create table mytab (id int primary key, " + 
>                                    "name varchar(50))");
>    :
>    s = con.createStatement();
>    DatabaseMetaData dbm = con.getMetaData();
>             
>    rs = dbm.getIndexInfo(null, null, "MYTAB", false, false);
>
>    while (rs.next()) {
>        System.out.println("Table: " + rs.getString(3) + " Index: " +
> rs.getString(6));
>        s.executeUpdate("alter table " + rs.getString(3) + " drop
> constraint "
>                        + rs.getString(6));
>    }
>
> Dag
>
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