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1992-06-04
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PRODUCT : Paradox NUMBER : 1063
VERSION : 4.0
OS : DOS
DATE : June 4, 1992 PAGE : 1/2
TITLE : An Explanation of Paradox 4.0 Locks
Intended Audience:
Paradox Network Users
Prerequisites:
A basic understanding of network and DOS rights, form locks, and
multi-table forms.
Purpose:__
An Explanation of Paradox 4.0 Locks
Paradox 4.0 has two new kinds of locks: a DIR lock and a GROUP
lock.
Dir Locks
The DIR lock permits a user to set the tables in a directory to
read-only status UNDER PARADOX. A user wishing to set a
directory lock must have full (read, write, create) access to
that directory. To set a DIR lock choose Tools | Net | Lock |
Dir Lock.
Once set, the DIR lock prevents all users (even the one who
placed it) from modifying the tables in the locked directory.
Only the user who set a DIR lock can remove it. A user wishing
to set a DIR lock may not specify his current private or working
directory. If you want to lock either your private or working
directory, you must first use Tools | Net | SetPrivate or Tools |
More | Directory, respectively, to change the directory
elsewhere, under the principle "You can't pull the rug out from
under your own feet". This also means that you can no longer use
a directory that has been DIR locked as a private directory,
since Paradox must have the ability to create temporary files in
a private directory.
BEWARE: A DIR Lock alone does not prevent anyone at the network
(operating system) level from deleting or creating files in the
locked directory. To ensure read-only status at the network
level, the tables in a directory must be designated read-only
using your network software. (See your network manual for more
information.) Generally, only a network supervisor will have
sufficient rights to do this.
PRODUCT : Paradox NUMBER : 1063
VERSION : 4.0
OS : DOS
DATE : June 4, 1992 PAGE : 2/2
TITLE : An Explanation of Paradox 4.0 Locks
If tables in the directory are set to read-only status at the
network level, applying a DIR Lock would be redundant. It is
also possible to use the DOS command ATTRIB +R command to
designate a given file as read-only (See your DOS manual for
more information on the ATTRIB command). Paradox 4.0 allows
users to view tables designated as read-only by the network or
DOS. Earlier versions of Paradox did not permit this.
Group Locks
Group locks are an improved replacement for form locks. Earlier
versions of Paradox used form locks to maintain referential
integrity of a multi-table form. A form lock required that all
changes be made using the same multi-table form. Group locks
remove this restriction and instead lock only the current master
record and its corresponding details.
Paradox creates a group lock in addition to a write record lock
any time a user coedits a linked multi-table form. Paradox
places a group lock on the detail records related to the current
master record, preventing other users from changing them.
Conversely, in a linked multi-table form, if a user coedits a
group of detail records, a write record lock is placed on the
associated master record to prevent other users from changing it.
This allows Paradox to maintain relational integrity even when
another user coedits the master or detail in table view or in
another form view, a situation which was impossible under 3.5
with form lock.
Paradox 4.0 does not permit editing of the primary key field in
the master if it is unable to place a group lock on all the
detail records. This can occur if another user is already
coediting one of the detail records. The reverse applies as
well: if the related master record cannot be record-locked,
Paradox does not permit editing of the detail records.
More information on locks can be found in the Paradox User's
Guide, under Chapter 11, "Modify", and Chapter 21, "Using Paradox
on a Network."