How to use system time to generate unique id?

[Nina]

I need to generate unique id for my application. Use system time to create
id, which is the best fit, but I don't know how to do it. Please help.

Thanks in advance for any input.

[Marina]

What about using the Guid class to generate a new Guid?

"Nina" <Ni**@discussio ns.microsoft.co m> wrote in message
news:36******** *************** ***********@mic rosoft.com...

I need to generate unique id for my application. Use system time to create
id, which is the best fit, but I don't know how to do it. Please help.

Thanks in advance for any input.

[Dave]

GUID is a good way to get a unique id but if you want your id to have some
relationship to the time why not try using the number of days, minutes, or
seconds since the file was created until it was last updated? Actually, I
beleive the applications productBuildPar t information gives you the number
of days since January 1, 2000 to the last day the file was modified?

System.Diagnost ics.FileVersion Info.GetVersion Info( _
System.Reflecti on.Assembly.Get ExecutingAssemb ly.Location).Pr oductBuildPart

If you want the time, in this case using minutes, between when the file was
created to when the file was last modified try -

System.IO.File. GetLastWriteTim e( _
System.Reflecti on.Assembly.Get ExecutingAssemb ly.Location).Su btract( _
System.IO.File. GetCreationTime ( _
System.Reflecti on.Assembly.Get ExecutingAssemb ly.Location)).T otalMinutes

Dave

"Nina" <Ni**@discussio ns.microsoft.co m> wrote in message
news:36******** *************** ***********@mic rosoft.com...

I need to generate unique id for my application. Use system time to create
id, which is the best fit, but I don't know how to do it. Please help.

Thanks in advance for any input.

[Herfried K. Wagner [MVP]]

"Nina" <Ni**@discussio ns.microsoft.co m> schrieb:

I need to generate unique id for my application. Use system time to create
id, which is the best fit, but I don't know how to do it.

The simplest solution is using a GUID:

\\\
Dim ID As String = Guid.NewGuid(). ToString()
///

--
M S Herfried K. Wagner
M V P <URL:http://dotnet.mvps.org/>
V B <URL:http://dotnet.mvps.org/dotnet/faqs/>

[Nina]

Thank you all for ideas and suggestions. Please tell me how does GUID work?
In case, user exits the application, and lunches the application again later,
could GUID generate same id that was generated in previous session? If this
could happen then I cannot use it.

"Herfried K. Wagner [MVP]" wrote:

"Nina" <Ni**@discussio ns.microsoft.co m> schrieb:

I need to generate unique id for my application. Use system time to create
id, which is the best fit, but I don't know how to do it.

The simplest solution is using a GUID:

\\\
Dim ID As String = Guid.NewGuid(). ToString()
///

--
M S Herfried K. Wagner
M V P <URL:http://dotnet.mvps.org/>
V B <URL:http://dotnet.mvps.org/dotnet/faqs/>

[Herfried K. Wagner [MVP]]

"Nina" <Ni**@discussio ns.microsoft.co m> schrieb:

Thank you all for ideas and suggestions. Please tell me how does GUID
work?
In case, user exits the application, and lunches the application again
later,
could GUID generate same id that was generated in previous session? If
this
could happen then I cannot use it.

That's very, very, very, ..., very unlikely. In practice it's "guaranteed "
that every GUID only occurs once. There are various parameters used to
calculate the GUID. So you can use a GUID as ID without any fear that
you'll get a GUID twice.

--
M S Herfried K. Wagner
M V P <URL:http://dotnet.mvps.org/>
V B <URL:http://dotnet.mvps.org/dotnet/faqs/>

[Nina]

Thanks again. The Id that generated by GUID is very long. Is there any way
that I can generate a unique id with a specific length?

"Herfried K. Wagner [MVP]" wrote:

"Nina" <Ni**@discussio ns.microsoft.co m> schrieb:

Thank you all for ideas and suggestions. Please tell me how does GUID
work?
In case, user exits the application, and lunches the application again
later,
could GUID generate same id that was generated in previous session? If
this
could happen then I cannot use it.

That's very, very, very, ..., very unlikely. In practice it's "guaranteed "
that every GUID only occurs once. There are various parameters used to
calculate the GUID. So you can use a GUID as ID without any fear that
you'll get a GUID twice.

--
M S Herfried K. Wagner
M V P <URL:http://dotnet.mvps.org/>
V B <URL:http://dotnet.mvps.org/dotnet/faqs/>

[Marina]

There is nothing stopping you from truncating it.

"Nina" <Ni**@discussio ns.microsoft.co m> wrote in message
news:D2******** *************** ***********@mic rosoft.com...

Thanks again. The Id that generated by GUID is very long. Is there any way that I can generate a unique id with a specific length?

"Herfried K. Wagner [MVP]" wrote:

"Nina" <Ni**@discussio ns.microsoft.co m> schrieb:

Thank you all for ideas and suggestions. Please tell me how does GUID
work?
In case, user exits the application, and lunches the application again
later,
could GUID generate same id that was generated in previous session? If this
could happen then I cannot use it.

That's very, very, very, ..., very unlikely. In practice it's "guaranteed " that every GUID only occurs once. There are various parameters used to
calculate the GUID. So you can use a GUID as ID without any fear that
you'll get a GUID twice.

--
M S Herfried K. Wagner
M V P <URL:http://dotnet.mvps.org/>
V B <URL:http://dotnet.mvps.org/dotnet/faqs/>

[Nina]

Thanks. Will truncate causing duplication?

"Marina" wrote:

There is nothing stopping you from truncating it.

"Nina" <Ni**@discussio ns.microsoft.co m> wrote in message
news:D2******** *************** ***********@mic rosoft.com...

Thanks again. The Id that generated by GUID is very long. Is there any

way

that I can generate a unique id with a specific length?

"Herfried K. Wagner [MVP]" wrote:

"Nina" <Ni**@discussio ns.microsoft.co m> schrieb:
> Thank you all for ideas and suggestions. Please tell me how does GUID
> work?
> In case, user exits the application, and lunches the application again
> later,
> could GUID generate same id that was generated in previous session? If > this
> could happen then I cannot use it.

That's very, very, very, ..., very unlikely. In practice it's "guaranteed " that every GUID only occurs once. There are various parameters used to
calculate the GUID. So you can use a GUID as ID without any fear that
you'll get a GUID twice.

--
M S Herfried K. Wagner
M V P <URL:http://dotnet.mvps.org/>
V B <URL:http://dotnet.mvps.org/dotnet/faqs/>

[Greg Burns]

If you truncated it, wouldn't that introduce the possiblity (albeit slight)
of non-uniqueness?

What if you didn't pass it around as a string, but kept it in its native
datatype? It is only 16 bytes in SQL server when stored as uniqueidentifie r
datatype. Versus the ~36 bytes for the equivalent string.

Greg

"Marina" <so*****@nospam .com> wrote in message
news:Oa******** ******@tk2msftn gp13.phx.gbl...

There is nothing stopping you from truncating it.

"Nina" <Ni**@discussio ns.microsoft.co m> wrote in message
news:D2******** *************** ***********@mic rosoft.com...

Thanks again. The Id that generated by GUID is very long. Is there any

way

that I can generate a unique id with a specific length?

"Herfried K. Wagner [MVP]" wrote:

> "Nina" <Ni**@discussio ns.microsoft.co m> schrieb:
> > Thank you all for ideas and suggestions. Please tell me how does
> > GUID
> > work?
> > In case, user exits the application, and lunches the application
> > again
> > later,
> > could GUID generate same id that was generated in previous session? If > > this
> > could happen then I cannot use it.
>
> That's very, very, very, ..., very unlikely. In practice it's "guaranteed " > that every GUID only occurs once. There are various parameters used to
> calculate the GUID. So you can use a GUID as ID without any fear that
> you'll get a GUID twice.
>
> --
> M S Herfried K. Wagner
> M V P <URL:http://dotnet.mvps.org/>
> V B <URL:http://dotnet.mvps.org/dotnet/faqs/>
>
>
>