Re: many-to-many with attributes?
Re: many-to-many with attributes?
- Subject: Re: many-to-many with attributes?
- From: Wolfram Stebel <email@hidden>
- Date: Tue, 26 Jul 2005 22:56:00 +0200
Am 26.07.2005 19:34 Uhr schrieb "Jim Zajkowski" unter
<email@hidden>:
> Hi there,
>
> What's the best way to handle a many-to-many relationship that has an
> attribute on the relation?
>
> That is, let's say I have a table of users, and a table of groups. I
> want a m-to-m relation between them, since clearly more than one user
> can belong to a group, and I'd like to see what users are in a group.
>
> But I also want to include some form of "access level" (e.g.,
> moderator, administrator, regular user).
>
> In DB land I'd model this by having an additional attribute on the
> users-groups table. But when I've done that in EOModeler, it creates
> a flattened relation, and so there isn't a way to see that attribute.
>
> So, what's the best way to do it? Not flatten the relation and walk
> the m-to-m by hand?
The answers you received up to now are not solving your problem.
I also missed a way to add an attribute to an relation and the possibility
to access and edit it.
I fetch it myself as can be seen below, so you need to know the primary keys
of the related objects, and you have a "cheep" fetch on one row, which you
Dipl. Inform. Wolfram Stebel, bugs&errors
Flutgrabenstr. 19, 35576 Wetzlar
Tel. 06441/47633
Mailto:email@hidden
Web: www.bugs-and-errors.de
can modify and save again.
If anybody knows better, let me know!
Wolfram
Sample:
Person<--->>group_person<<--->group
^
^
|
|
|
v
Function_Key
Setting and getting Function_Key from Group is as follows:
public EOGenericRecord getFunktionKey ( EOEditingContext ec, CPerson
aPerson )
{
if ( NSLog.debugLoggingAllowedForLevel ( NSLog.DebugLevelDetailed )
)
{
NSLog.out.appendln ( EOUtilities.primaryKeyForObject ( ec,
aPerson ) );
NSLog.out.appendln ( EOUtilities.primaryKeyForObject ( ec, this
) );
}
NSMutableDictionary aDict = new NSMutableDictionary ();
aDict.takeValueForKey ( aPerson, "person" );
aDict.takeValueForKey ( this, "groups" );
NSArray result =
EOUtilities.objectsWithFetchSpecificationAndBindings ( ec, "Group_Person",
"onePersonForGroup", aDict );
if ( ( result == null ) || ( result.count () != 1 ) )
{
// should not happen
if ( NSLog.debugLoggingAllowedForLevel (
NSLog.DebugLevelDetailed ) )
{
NSLog.out.appendln ( "missing relation for : " +
aPerson.name () );
}
return null;
}
else
{
EOGenericRecord eo = ( EOGenericRecord ) result.objectAtIndex (
0 );
return ( ( EOGenericRecord ) eo.valueForKey ( "function_key" )
);
}
}
public void setFunctionKey ( EOEditingContext ec, CPerson aPerson,
EOGenericRecord functionKey )
{
if ( NSLog.debugLoggingAllowedForLevel ( NSLog.DebugLevelDetailed )
)
{
NSLog.out.appendln ( EOUtilities.primaryKeyForObject ( ec,
aPerson ) );
NSLog.out.appendln ( EOUtilities.primaryKeyForObject ( ec, this
) );
}
NSMutableDictionary aDict = new NSMutableDictionary ();
aDict.takeValueForKey ( aPerson, "person" );
aDict.takeValueForKey ( this, "groups" );
NSArray result =
EOUtilities.objectsWithFetchSpecificationAndBindings ( ec, "Group_Person",
"onePersonForGroup", aDict );
if ( ( result == null ) || ( result.count () != 1 ) )
{
// should not happen
if ( NSLog.debugLoggingAllowedForLevel (
NSLog.DebugLevelDetailed ) )
{
NSLog.out.appendln ( "missing relation for : " +
aPerson.name () );
}
}
else
{
EOGenericRecord eo = ( EOGenericRecord ) result.objectAtIndex (
0 );
eo.takeValueForKey ( functionKey, "function_key" );
}
}
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