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I've never heard of it. What is it? Sounds like some kind of lightweight design approach.
"The clue train passed his station without stopping." - John Simmons / outlaw programmer
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Paul Conrad wrote: I've never heard of it. What is it? Sounds like some kind of lightweight design approach.
...for a large numbers of objects, see, for instance http://en.wikipedia.org/wiki/Flyweight_pattern[^]
If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler.
-- Alfonso the Wise, 13th Century King of Castile.
[my articles]
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I´m trying to create a windows application that will be able to store data in a database. Both the application and the database have to be in one installation package and the end user has to be able to use the application correctly without the need to install anything else(database server,...). Can anyone help me with this? Which kind of database should I use?
I was thinkink about using MSSQL 2005 Exress Edition and then just attached the .mdf file to the application, but I´m not sure if this is the best solution. Is it possible to access and work with .mdf file on a computer, that does not have the MSSQL server installed?
Or what is the best solution for this problem?
cellardoor
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SQL Server Compact Edition[^] is what you need. (Express still needs to be installed.) Compact is just a couple of dlls that let you use a single .sdf file as a database. Similar limits to Express (4gig db limit etc) - but it is also missing stored procs.
Then use this[^] to handle your data access and the whole data end of your application is done for you.
Your other option if you don't actually need the databasey features of a database is to use a prevalence mechanism[^] that stores plain .net objects for you.
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Thank you, I´ll try the SQL Server Compact Edition.
cellardoor
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I have a hierarchy of objects that share some attributes, e.g. both my parent Record and Column objects have a columnDelimiter property. I want this property on the Column object to default to the same property on the Record object, until specified on the Column object. What is the best way to go about this? I could give each Column a reference to the Record it belongs to, but this seems not quite right to me. My other option is to have the Record act as a ColumnFactory, setting the columnDelimiter value on each Column it creates, until a set accessor on Column optionally overrides that default value.
Calling all South African developers! Your participation in this local dev community will be mutually beneficial, to you and us.
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I am having trouble understanding your problem. Can you provide a scenario where the column delimiter is different from the record delimiter?
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No, maybe that was a bad example, but I'm trying to build in forward compatibility with SSIS, and their columns all define their own delimiters. However, my problem is not one of Column specified column delimiters and Record specified column delimiters; it is one of child objects 'inheriting' property values from their parents, until or unless the child object overrides the value.
I do have exactly the same requirement for individual Columns to have an option to quote their contents, which overrides the 'quote contents' option for the Record.
Calling all South African developers! Your participation in this local dev community will be mutually beneficial, to you and us.
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Brady Kelly wrote: I'm trying to build in forward compatibility with SSIS
I don't know what that means.
Brady Kelly wrote: I do have exactly the same requirement for individual Columns to have an option to quote their contents, which overrides the 'quote contents' option for the Record.
Sorry, I just don't get it.
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OK, Record is my parent object (not base object), and it has a collection of child Column objects. Record has a boolean property, QualifyText, which when set, surrounds string columns with a configured qualifying character. Column, a child object, also has a QualifyText property. If this property is set on a Column object, the export engine must use the QualifyText property set for that Column object. When the QualifyText property is null on a Column object, the export engine must use the value of the QualifyText property on the parent Record of a column.
Calling all South African developers! Your participation in this local dev community will be mutually beneficial, to you and us.
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Brady, it's possible we are at an impasse on design fundamentals.
Perhaps I am having difficulty providing any suggestions of how to deal with your problem as you have framed it because I see a larger problem in your design. Things like your previous statement...
Brady Kelly wrote: I have a hierarchy of objects that share some attributes
... point to fundamental design flaws for me.
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Mike, I think the problem is with my description, not my design. I am looking to implement something somebody likened to Ambient Properties[^]. If I don't specify a background colour for an edit control I place on a container, I would like that control to assume the background colour of its container. If don't specify a QualifyText flag for a Column, I want the consumer of the Column object to use the QualifyText flag of its parent, the Record. I want to keep this logic encapsulated in the code that defines Record or Column, not in the code that uses them. There may be more purist ways of doing this, but it is by no means an abominable design requirement.
Calling all South African developers! Your participation in this local dev community will be mutually beneficial, to you and us.
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Thanks, I am finding them interesting, but have to continue tomorrow. It's now 23h40 here and I'm going home.
Calling all South African developers! Your participation in this local dev community will be mutually beneficial, to you and us.
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Does that guy really advocate not using properties?
I think it's a bit bizzare as i rely on properties for injections via routes other than constructors. Sure they don't get used much at higher levels, but for primitive types they are essential. Generally tho, i can't agree.
I'm guessing the guy asking the questions is trying to implement something along the same lines as the VS designer with inherited attributes for defaults, whether or not its appropriate for his domain is another thing entirely.
-------------------------------
Carrier Bags - 21st Century Tumbleweed.
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Tristan Rhodes wrote: Does that guy really advocate not using properties?
It's slightly more complicated than that. If you read Holub's article I would start by saying he has far more experience and skill than I will ever have. Also his writing is far superior to mine, therefore my attempt to clarify his words seems silly but here goes.
I work with people who think that just because the code they write has classes in it they are doing object oriented programming. Nothing could be further from the truth. That is what Holub's point is. Just because you write a class doesn't mean you are doing object oriented "design".
Holub points out that many people are doing just that. They write a class making the attributes private (data hiding) good start, but then they expose them, and worse "use them" from other classes thereby reversing the "hidden" aspect of the data.
Again the point is not to not use properties it's to wake up and try to understand the point of "data hiding", what the benefits are and why it's a "principle" of Object Oriented Design. Basically all you do when resort to using public properties is give up on that principle of OOD and fall back to procedural design. Along with that decision you incur the technical debt[^] that comes with it. The technical debt is the reason it's bad, it's not a religious argument it's a practical argument. That's why it doesn't matter if you or anyone else agrees with Holub, all that matters is reality and he has a better grip on it, when it comes to software development, than most of us.
Well that's my two cents worth and that's about all it's worth, I doubt it is helpful to you or anyone else.
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Ok, i think i get it, but i need some concrete examples.
For instance - the class below has a reasonable use of properties.
<br />
class Validator<br />
{<br />
<br />
<br />
public bool _Valid<br />
{<br />
get{return _isValid;}<br />
}<br />
}<br />
However, if you have the following, you are breaking the encapsulation of the IsValid value, and moving what should be internal logic to outside the class:
<br />
<br />
class Validator<br />
{<br />
<br />
<br />
public bool _Valid<br />
{<br />
get{return _isValid;}<br />
set{_isValid = value;}<br />
}<br />
<br />
<br />
}<br />
<br />
(Ok, i REALLY had to think for that second example)
Does that sound about right?
T
-------------------------------
Carrier Bags - 21st Century Tumbleweed.
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Tristan Rhodes wrote: Does that sound about right?
Realize this issue is about Object Oriented Design. For most of us we are students for a long time, maybe forever. Don’t expect to obtain a 100% understanding in a few days. In the concrete example you posted you have focused on the idea that exposing the data through a setter is where the design goes off track. It is an indication of a poor design, it’s not “the” problem. A more complete analysis is required. What is the purpose of the Validator class? Having a class that just determines the Boolean state and then simply exposes the state might indicate a larger design issue. Other elements of the design must be considered to know the answer.
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I’m seeking ideas for an efficient technique to sequence transactions in a SQLServer table for consumption by a serviced component app-server running on several physical machines. Currently the component app-server is selecting “TOP 1” transaction primary key from the table and inserting it into a logical locking table with an expiration timestamp and the current machine name. The “TOP 1” selection also excludes transactions where the primary key is already in the logical locking table for another physical machine where the expiration date stamp has not yet expired.
The table locks on the "logical locking" table during logical lock inserts is limiting concurrency but this is the only method I could think of to ensure each server is processing a unique row in the table.
Thanks
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Anubis333 wrote: efficient technique to sequence transactions in a SQLServer table for consumption by a serviced component app-server running on several physical machines.
What if you have already painted yourself into a corner? What problem are you trying to solve? I could guess based on your post, but if wrong, it's a waste of time.
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If it takes a server 60 minutes to process one transaction, I could increase the transactions per hour by running 20 transactions on 20 different servers at the same time. The problem I’m trying to solve is, I'm trying to find an efficient way to allow distributed processing of independent transactions on multiple machines. The result being the same transaction is not processed more than once on the other 19 servers. In short, the original question I asked is the problem I’m trying to solve.
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Anubis333 wrote: I'm trying to find an efficient way
Anubis333 wrote: The table locks on the "logical locking" table during logical lock inserts is limiting concurrency
So there is an efficiency problem with your current solution?
Anubis333 wrote: If it takes a server 60 minutes to process one transaction
It's difficult to believe that any time required for the database to execute table locks could significantly deteriorate a 60 minute transaction? 
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 The 60 minutes thing was a hypothetical situation to help define what I was trying to accomplish, it had nothing to do with my current solution. I wasn’t seeking critiques on my current solution only ideas for a better/different method of achieving the same goal. As always, I’m getting responses on everything except the question at hand.
The question at hand being, "I’m seeking ideas for an efficient technique to sequence transactions in a SQLServer table for consumption by a serviced component app-server running on several physical machines"
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Hi,
I have a database used for storing information about our machines. I have tables for machine configuration, utilisation history, schedules etc.
I'm currently working on a tool an extension to the database where supervisors will be able to open and view the schedule for a specfic machine, make changes, and save it.
The problem is that obviously I don't want two different users to be able to open a schedule at the same time(or both could save and overwrite each others changes), so I need to somehow lock the schedules.
What i've thought of doing is including a Lock table, that contains uniqueId's of locked schedules, so before opening a schedule, the lock table is checked and if the schedule is locked, the open is cancelled. Or if the schedule is free, a lock row is inserted and the user is allowed to open the schedule. Problem is, what happens if a user's PC loses power while they have a schedule open. That would mean that the schdeule would remain locked forever. So next i considered adding an ExpiryTime to a lock. So if a user crashed out, the lock would expire after a few minutes. But that means that the app will have to constantly refresh the lock to stop it expiring while the use has the schedule open. I'm not too keen on this idea either. What if the users pc just slowed up and they couldn't refresh the lock in time. I'd then have to handle kicking them out and they'd lose any changes.
The other problem is that we also have some wireless laptops, so sometimes, connections to the database are intermittant. How can I implement this so if the connection is lost for a minute or two, the users work isn't?
Is there any standard pattern for implementing this kind of thing? It must be a common requirement. Can anyone suggest any ideas or point me in the right direction. Has anyone implemented this kind of system before and can suggest a proven technique?
Alternativly, is there functionality within SQL server to implement this kind of thing. I'm not just talking about row locking as a schedule will consist of many jobs, each consisting of many products and the quantities required of each product, so a "schedule" will span multiple tables.
Thanks
Simon
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