This article demonstrates how to “roll your own” surrogate keys and sequences in a platform-independent way, using standard SQL.
C# code to get Unique ID for a computer that be use as licences key. Using System; using System.Management; using System.Security.Cryptography; using System.Security; using System.Collections; using System.Text; namespace Security /// /// Generates a 16 byte Unique. Generating license keys for your own products. Use this information to find out how to generate software license keys to allow access to your own products. If any of your own products require keyed compliance, you need to create software license keys for them. A valid license key for each of these products must be loaded on the system so that.
Surrogate keys
Relational theory talks about something called a “candidate key.” In SQL terms, a candidate key is any combination of columns that uniquely identifies a row (SQL and the relational model aren’t the same thing, but I’ll put that aside for this article). The data’s primary key is the minimal candidate key. Many people think a primary key is something the DBA defines, but that’s not true. The primary key is a property of the data, not the table that holds the data.
Unfortunately, the minimal candidate key is sometimes not a good primary key in the real world. For example, if the primary key is 6 columns wide and I need to refer to a row from another table, it’s impractical to make a 6-column wide foreign key. For this reason, database designers sometimes introduce a surrogate key, which uniquely identifies every row in the table and is “more minimal” than the inherently unique aspect of the data. The usual choice is a monotonically increasing integer, which is small and easy to use in foreign keys.
Every RDBMS of which I’m aware offers a feature to make surrogate keys easier by automatically generating the next larger value upon insert. In SQL Server, it’s called an
IDENTITY column. In MySQL, it’s called AUTO_INCREMENT . It’s possible to generate the value in SQL, but it’s easier and generally safer to let the RDBMS do it instead. This does lead to some issues itself, such as the need to find out the value that was generated by the last insertion, but those are usually not hard to solve (LAST_INSERT_ID() and similar functions, for example).
It’s sometimes desirable not to use the provided feature. For instance, I might want to be sure I always use the next available number. In that case, I can’t use the built-in features, because they don’t generate the next available number under some circumstances. For example, SQL Server doesn’t decrement the internal counter when transactions are rolled back, leaving holes in the data (see my article on finding missing numbers in a sequence). Neither MySQL nor SQL Server decrements the counter when rows are deleted.
In these cases, it’s possible to generate the next value in the insert statement. Suppose my table looks like this:
The next value for
c1 is simply the maximum value + 1. If there is no maximum value, it is 1, which is the same as 0 + 1.
There are platform-dependent ways to write that statement as well, such as using SQL Server’s
ISNULL function or MySQL’s IFNULL . This code can be combined into an INSERT statement, such as the following statement to insert 3 into the second column:
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The code above is a single atomic statement and will prevent any two concurrent inserts from getting the same value for
c1 . It is not safe to find the next value in one statement and use it in another, unless both statements are in a transaction. I would consider that a bad idea, though. There’s no need for a transaction in the statement above.
Downsides to this approach are inability to find the value of
c1 immediately after inserting, and inability to insert multiple rows at once. The first problem is inherently caused by inserting meaningless data, and is always a problem, even with the built-in surrogate keys where the RDBMS provides a mechanism to retrieve the value.
Sequences: a better surrogate key
Surrogate keys are often considered very bad practice, for a variety of good reasons I won’t discuss here. Sometimes, though, there is just nothing for it but to artificially unique-ify the data. In these cases, a sequence number can often be a less evil approach. A sequence is just a surrogate key that restarts at 1 for each group of related records. For example, consider a table of log entries related to records in my
t1 table:
At this point I might want to enter some more records (0, 11) into
t1 :
Now suppose I want the following three log entries for the first row in
t1 :
There’s no good primary key in this data. I will have to add a surrogate key. It might seem I could add a date-time column instead, but that’s a dangerous design. It breaks as soon as two records are inserted within a timespan less than the maximum resolution of the data type. It also breaks if two records are inserted in a single transaction where the time is consistent from the first to the last statement. I’m much happier with a sequence column. The following statement will insert the log records as desired:
If I want to enter a log record on another record in
t1 , the sequence will start at 1 for it:
MySQL actually allows an
AUTO_INCREMENT value to serve as a sequence for certain table types (MyISAM and BDB). To do tihs, just make the column the last column in a multi-column primary key. I’m not aware of any other RDBMS that does this.
You use the PSCipherJava utility's
buildkey command to build new Triple DES encryption keys.The buildkey command adds a new Triple DES encryption key stored in the psvaultfile (the key file). If you generate new versions of the key file,the system appends the new version of the key to the end of the keyfile.
To invoke the commandon a Windows server, change to the directory where PSCipher residesand enter:
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To invoke the commandon UNIX, change to the directory where PSCipher resides and enter:
Select one web serverin your system to generate the new version of the key file. The pscipher.batand PSCipher.sh utilities only run in the Java environment of theweb server. After you have created the new key file, you then copythe new version of psvault from the initial server to the appropriatedirectories on all the appropriate servers in your system. The psvaultfile is stored in different directories depending on your web servervender (as described in the following sections). On the applicationserver the psvault file resides in <PS_HOME>secvault.
Note: If you are not usingthe default encryption key and you have generated a unique encryptionkey, note that each time you add a new server to your system, youwill need to copy the key file to the appropriate location on thatserver. For example, if you are using the default key version ({V1.1}),any server you add to the system and install PeopleTools on will alsohave the default key version ({V1.1}). As such, no further steps arerequired. However, if you have generated a new key, giving the versionnumber a value of {V1.2} or greater, then you need to make sure tocopy that key file to the added server(s). Also, each time you updatethe key, you need to ensure that the new version of the key file iscopied to the additional servers in your system.
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Warning! When you upgrade tonew PeopleTools releases, as in PeopleTools 8.48 to PeopleTools 8.50,you will need to backup any modifications you have made to the keyfile using PSCipher in the previous release and reapply that samekey file to the appropriate servers onto which you have installedthe new PeopleTools release.
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