|
I agree that seeing a difference in a schema does not tell you how you got there, but the simple matter of detecting a change will initiate an investigation.
No change = No problem (ideally)
Change = Investigation
When there is team development on an application there must be communication among the team to reflect any changes. Using a source control system like Subversion is a good way to see changes made and designating a single person as the responsible party for making any changes to the schema is also a good idea.
|
|
|
|
|
David Mujica wrote: My response gave a viable option for him to determine the difference between tables in two databases. I did not try to read into the 'why' or 'what for'.
Good point; yet there are certain dangers to the approach, which should also be mentioned if one is to make an informed decision.
It's good to see a broad variety of answers, each with their own motivation. You're right that my comment was superfluous after the warning of PIEBALD, and reading back it indeed looks a tad patronizing.
David Mujica wrote: There is no reason to be sarcastic when replying. Just stay professional.
..will try, a little bit harder. Then again, sarcasm is an efficient way to get a point across and to create a few seconds of shock in which one contemplates the previously ignored point.
Bastard Programmer from Hell 
if you can't read my code, try converting it here[^]
|
|
|
|
|
I always appreciate the help I get from the folks here.
Sometimes I have to resist jumping on the dog-pile. There are many posts that I just don't respond to because they are just not worth my time.
Thanks again for your (and others) contribution to the community; I've learned a lot here.
David
|
|
|
|
|
You attend project meetings where the DBA tells you.
|
|
|
|
|
I agree with PIEBALD; you do not know why the columns are altered, so best idea is to ignore the changes, and declare "incompatibility with the current version" if they're not as you expected them to be.
If a column is added, it's not always desired to have it visible; if it is visible, it will have consequences for the layout, which means some changes to reports.
If a column is deleted, it's not always desired to ignore it; it could have been renamed during an update, with the intention of renaming it back later - your behaviour would hide a very important bug.
Bastard Programmer from Hell
if you can't read my code, try converting it here[^]
|
|
|
|
|
I want to know whether it contains data.If not ,it's easy.
|
|
|
|
|
|
Hello,
I want to store the recent measuring results as well as control samples of older measurements persitently on disk so that the last state can be restored even in the case of a power loss. To make loading the data on startup not unnecessary slow, I want to remove the old, unneeded data from the list.
This means that the measuring results will be continuously appended to the list, but the time when it will be removed is not known in advance.
Would you recommend using a database (ideally some compact system like SQLite so that the user does not have to install a databse server) for this, or are there alternatives?
My idea would be to store the measuring results in one table, using the measuring time as key. In another table, the keys for the last n measuring results would be stored and in a third table the keys of the control samples. If the entries of the first table are not referenced any more from the two other tables, the measuring results should be automatically removed. Is there some concept to acchieve this?
Alex
|
|
|
|
|
This decision should be driven by volume and usage. If you are only processing a few hundred records and do not need to massage the data then an XML or csv file store would be acceptable. Otherwise go for a database.
Why make it complex with multiple tables if you are using text/xml, simply load the entire file into memory and manipulate the collection. Write the collection to the file at regular intervals.
A lot will depend on the criticallity of the data and the frequency of the reads!
Never underestimate the power of human stupidity
RAH
|
|
|
|
|
Thank you for your answer.
In a previous version, we wrote the complete XML file - however, due to the relative large amount of data (and the limited resources, as it is an embedded system) - this will not be possible in the final release. So I think the database is the most promising.
Which leaves me with the other questions, how to implement this as a weak reference pattern.
Alex
|
|
|
|
|
LionAM wrote: how to implement this as a weak reference pattern.
Databases generally do not directly support the equivalent of weak reference pattern.
One solution is to append the data as needed in a database table and then run a program in background periodically and check for "old" data and purge them from the database. What "old" means and the frequency of purging depends on the volume of your data.
|
|
|
|
|
As a database kind of guy, I strongly recommend a database.
LionAM wrote: To make loading the data on startup not unnecessary slow
I asssume you do this to show a graph or similar of the recent trend, otherwise I don't see why you would load old data. A database makes this easy by allowing you to query only the recent data. You could sort the data descending by date and take only the top n records or you could query the records where the timestamp is greater than the current time minus soome number of minutes or hours. Or you could purge data out of the table after some period (perhaps after summarizing it into another for historical reasons).
Also, as I don't know what sorts of "measuring results" you are dealing with I'll pass along a concept that you may find useful. It's sort of a data compression technique whereby if the measurements don't change much you don't store every individual measurement. For instance, the temperature of a commercial oven for baking bread or cookies needs to be monitored, it can probably vary a little (let's say a tenth of a degree) from the target temperature without causing an alarm, but if it changes a whole degree (for instance) it should be noted. Furthermore, if the temperature stays close to the target temperature for hours on end (as it should) we do want to log some readings (perhaps at least every fifteen minutes). For these reasons, you may want to develop a system that will only store a reading if the difference from the previous stored reading is outside some specified range or if some specified time span has elapsed.
|
|
|
|
|
In principle, this is exactly what I want - store a live view of a certain time span as well as the status of several control charts. As the statistical spread of the measurement results is of great interest, it makes no sense to store only large fluctuations (then it would perhaps be too late to countersteer ...).
As the data is only used to restore the last program state and therefore stored locally (there is a separate export feature), I would prefer some compact database (without a database server). Which would you recommend? SQLite?
Alex
|
|
|
|
|
LionAM wrote: it makes no sense to store only large fluctuations
You can set the thresholds as appropriate.
LionAM wrote: some compact database
I've dabbled in Sql Server Compact Edition recently, but I can't really give an informed recommendation.
You could also consider serializing the current state to a file periodically.
Maybe my LimitedQueue[^] could be of use to you.
|
|
|
|
|
LionAM wrote: SQLite?
I'd recommend programming against the IDbInterfaces, and actually time/test the various databases that you would want to consider.
- Sqlite is good in terms of performance, once you take in account that everything is in a transaction.
- SqlCe is more integrated into .NET, and would be the preferred option if you plan to synchronize to Sql Server.
- Microsoft Access would be a sweet idea if your client has Office, and if the primary goal of the data is to show reports.
- Excel would work too, almost as fast as Access, and can be accessed over ADO.NET; Not an obvious choice as a datastore, but still very nice for charts.
Bastard Programmer from Hell 
if you can't read my code, try converting it here[^]
|
|
|
|
|
Eddy Vluggen wrote: xcel would work too, almost as fast as Access, and can be accessed over ADO.NET;
Not an obvious choice as a datastore, but still very nice for charts.
And if the primary goal of the data is to be accessed by accountants. 
|
|
|
|
|
Thank you for your answer.
The data is used only to restore the last program state. There is an additional export feature - so I think SQLite ore SQL CE will achieve what I want.
Alex
|
|
|
|
|
Hallo,
I cannot connect to MySQL database from PC outside home network.
I created client aplication in c++ to editing data in MySQL database.
We have 2 PC at home. Both PC has the same TCP/IP address like xxx.xx.xx.xx.
PC with MySQL server has IPv4 address 10.10.11.93. I tried to type xxx.xx.xx.xx/10.10.11.93 but
error is occurred: 2005: unknown MySQL server host "xxx.xx.xx.xx/10.10.11.93" ( 11004).
I can connect to the database from second PC at home wrighting the name of PC with MySQL server.
What I have to write to connect from outside?
Thanks.
|
|
|
|
|
1.fcb1913 wrote: What I have to write to connect from outside?
In a default-installation, it's not possible to make a connection to the server from the outside world. The idea behind that being that you can install a server, without having to worry about me poking at the password over the internet.
You'll have to check the local firewall, and, if it's a home-PC, your router. If that last is the case, you can go to this site[^], and click on "More about you" on the left; it'll load a new page, hopefully with a hostname. If not, you can still connect using the IP-adress, given that the server is configured and reachable.
Bastard Programmer from Hell
if you can't read my code, try converting it here[^]
|
|
|
|
|
On MySQL server is enabled TCP/IP networking, firewall exception for port and enabled root access from remoute machines. I know my TCP/IP - is static.
If I'm trying to connect from outside home network, a firewall don't notice anything.
I can connect from another PC at home network. What I have to do to connect from outside?
|
|
|
|
|
1.fcb1913 wrote: What I have to do to connect from outside?
I suggest you run a little webserver, and use that to verify whether you can connect. If you can't serve a page from the machine, then you won't be able to use a database remotely.
The logical steps would be something like
- verify connectivity
- verify db-server is running
- verify local connectivity
- verify remote connectivity
If your PC is "at home", chances are your router has it's own firewall. Check the manual to verify - the router-setup varies per product. I changed something called "NAT", pointing from the outside to the static IP on the inside-network.
(The numbers inside the network should be different from those outside, and you'd be using the outside-number to connect)
Bastard Programmer from Hell
if you can't read my code, try converting it here[^]
|
|
|
|
|
1.fcb1913 wrote: server has IPv4 address 10.10.11.93. I
That is a private IP address.
It is NOT possible to address a private IP address on the internet. There is absolutely no way to do it.
Your options are
- Figure out your public IP address, which your ISP has given you. There is NO guarantee that you have a public IP address. However if you have one then your cable modem would be the one that has it. You would need to set up your modem to redirect requests to your box.
- Buy a public IP from your ISP. Then do the above.
|
|
|
|
|
Thanks.
I have public IP address.
On a chimney we have white cubic transmitter-receiver and one cable ended with a switch from witch the computers are connected.
I don't know if it is router or modem.
I tried typed my public IP address, IPv4 address, gate IPv4 and server DNS IPv4 address into web browser to set up connection,
but always connect error is occured. I have contacted my internet provider, I hope he'll resolve this.
|
|
|
|
|
Have you tried using port forwarding as Bernhard has suggested?
"Any sort of work in VB6 is bound to provide several WTF moments." - Christian Graus
|
|
|
|
|
Depending on the hardware for connecting your local intranet to the internet, it may be possible to set-up a "port forwarding": that means, you send the request to your public ip address with a port specified, and the router then forwards the request to an internal computer and that port. To get your public ip address, you can use tools like dyndns.
|
|
|
|
General 
News 
Suggestion 
Question 
Bug 
Answer 
Joke 
Praise 
Rant 
Admin 
Submit an article or tip
