I'm rewriting an older-than-dirt MFC application, ripping out the old MFC-based DB code and re-working queries to make it run faster. This code works with a MS Access 2003 .mdb file.
The old code used the convenience functions like RFX_Bool, RFX_Long, RFX_Int to read from the records. These are nice, and I am reading about binding in ODBC using SQLBindCol to set the bindings ahead of time to avoid that extra processing time for each row. This is great, but I see SQLBindCol only takes the column number, not the name. What if I want to bind using the column name like with the RFX_* functions? SQLDescribeCol gives the column names, but it doesn't have the "full" name, i.e. [Table/Alias].[Column]. Some of my queries involve JOIN'ing the same table multiple times with aliases, so I can't bind the column by the column name alone. If I plug my query into Access, the Datasheet view shows the alias in the column name. I'm currently using my connection string with Driver={Microsoft Access Driver (*.mdb, *.accdb)}, if it matters.
tl;dr How do I do MFC's RFX_*(fieldExchange, L"[Table].[Column]", &variable) in the modern ODBC API?
OK, I think I understand what the RFX functions are doing now, and I think I know what I need to do.
The MFC ODBC classes construct your query programmatically, so after starting with SELECT, UPDATE, etc, every call to RFX_* simply appends the field name to the query, then ties a reference to your variable to the column index, which it increments after every call. So I just need to append my fields to my queries with a helper function the same way MFC does, in order to bind my pointers in the same way MFC does.
Hopefully this is helpful to somebody.
Related
I have about 500 fixed width columns in a flat file that I want to apply the same logic to to replace an empty column with null before it goes into the database.
I know the command to replace the empty string with null but I really don't want to have to use the gui to input that command for every column.
So is there a tool out there that can do this all on the back end?
You could look at something like the EzAPI to create your data flow. This this answer, I have an example of how one creates a EzDerivedColumn and sets the formula within it.
Automatically mapping columns with EZApi with OLEDBSource
If you can install third party components, I've seen a number of implementations of a Trim-To-Null functionality on codeplex.com
BIML might be an option to generate your package as well. I'd need to play with that to figure the syntax though.
My googlefu worked a little better after lunch.
I as able to modify about the 5th comment down on http://social.msdn.microsoft.com/Forums/sqlserver/en-US/222e70f5-0a21-4bb8-a3fc-3f365d9c701f/ssis-custom-component-derivedcolumn-programmatically-problems?forum=sqlintegrationservices to work for my needs.
My c# code will now loop through all the input columns from a "Flat File Source" object and add a derived column for each.
I have been developing programs in VB.NET for a few years and am familiar with it. The area where I do not have a lot of exposure is databases.
I am writing a program (for my personal use) called movie manager. It will store information on movies I have. I have selected Sql Server Compact Edition database. Assume I have a database with two tables namely Info and Cast. Info table has a few columns such as movie_name, release_date and so on. Cast table has few cols such as first_name,last_name etc.
Right now I have created a DataSet which reads all the info of tables from database (opens connection, fills tables info, closes connection). This way in a global variable I have a snapshot of database.
My queries :
Once I have data with me, every time I need to add, edit or delete a record I have to open a connection, fire an sql and close the connection. Right ? Is there a way to do this without using Sql ? Plus is this concept okay.
Since I am not using structures so I need to create empty datasets to store temp information. Is this convenient ?
If I have to search for a specific thing in dataset table, then do I have to loop thru all items or can I use sql on dataset or is there an alternate ?
1)Once I have data with me, every time I need to add, edit or delete a record I have to open a connection, fire an sql and close the connection. Right ? Is there a way to do this without using Sql ? Plus is this concept okay.
No. To update a database, you have to use the database. Create a stored procedure in the database to handle your functionality and then call it from the code and pass in whatever data needs saved. DO NOT USE INLINE SQL. Paramterized stored procedures are the way to go.
2) Since I am not using structures so I need to create empty datasets to store temp information. Is this convenient ?
It depends on what you're doing. I would create an object model to retain my updated data and then I'd pass the properties into the stored procedure when it was time to save my changes.
3) If I have to search for a specific thing in dataset table, then do I have to loop thru all items or can I use sql on dataset or is there an alternate ?
You can loop the rows or you can use linq to pull what you need out. Linq is really nice as it's basically .NET coded queries against a collection.
There are plenty of tutorials/guides out there to show you how to update via stored proc call form your code. There are a ton of linq tutorials as well. Basically, a linq query against your table will look something like:
dim result as Generic.List(of String) =
(from r in table.AsEnumerable()
select r
where r["columnName"] = "the value").ToList()
This syntax is probably a bit off, but it looks something like that.
Edit
Your Model:
Public Class EmployeeModel
Public Property Id
Public Property FirstName
Public Property Last Name
Public Property JobCode
Public Sub EmployeeModel(your params)
//set properties
End Sub
End Class
Your DAL:
Public Shared Class EmployeeDAL
Public Shared Sub SaveEmployee(ByRef model as EmployeeModel)
// call your sp_SaveEmployee stored procedure and set the parameters to the model properties
// #id = EmpoyeeModel.Id
// #JobCode = Employee.JobCode
// ...
End Sub
End Class
I use VB every few months, so there are probably some small syntax errors in there. But that's basically all you need to do. The function to save your data is in the DAL, not in the class itself. If you don't want to use a DAL, you can put the save functionality in your class, though. It'll work the same way, it's just not as clearly separated.
On your Questions.
number 1: You have to connect to database in order to store and retrieve data. There are lots of ways on how to deal with it and one way of it is to use app.config or you may simply create a function that calls the connection every time you need it.
number 2: Since you are dealing with dataset here are some tips you might want to look at DataSet
number 3: You can also try using Data Adapter and Data Table. I am not sure what you meant by your question number 3.
Cheers
I have problem with the way you are using your database and the ram of your computer.
Problem1: since you already have a database for holding the movies information why are you again holding the same information in memory?, creating an extra overhead. if your answer is for performance or i have cheap memory then why don't you use xml or flatfile instead? Database is not needed with this senario.
Problem2: You are like a soldier who dosent know about the weapon he use? right? because you are asking silly questions your first question about opening connection.. the answer is yes you have to open the connection every time save/read the data and close it as soon as possible.
your second question about convinent the answer is no. instead create class with all field as property and some method for initialization,saving,deleting. this way you have to write less code. nad suppose you have a movie names xyz there can be another movie xyz how will you distinguish it? if you have whole information b4 you you can do it via release date ,casts etc, but still it will be hard, so create a primary key for both your table
and finally your 3rd question , it will be easier to use use sql queries than looping thru the dataset(get rid of the dataset as soon as possible)
wish yu good luck on the road to rdbms
I'm working on a data conversion utility which can push data from one master database out to a number of different databases. The utility its self will have no knowledge of how data is kept in the destination (table structure), but I would like to provide writing a SQL statement to return data from the destination using a complex SQL query with multiple join statements. As long as the data is in a standardized format that the utility can recognize (field names) in an ADO query.
What I would like to do is then modify the live data in this ADO Query. However, since there are multiple join statements, I'm not sure if it's possible to do this. I know at least with BDE (I've never used BDE), it was very strict and you had to return all fields (*) and such. ADO I know is more flexible, but I don't know quite how flexible in this case.
Is it supposed to be possible to modify data in a TADOQuery in this manner, when the results include fields from different tables? And even if so, suppose I want to append a new record to the end (TADOQuery.Append). Would it append to two different tables?
The actual primary table I'm selecting from has a complimentary table which is joined by the same primary key field, one is a "Small" table (brief info) and the other is a "Detail" table (more info for each record in Small table). So, a typical statement would include something like this:
select ts.record_uid, ts.SomeField, td.SomeOtherField from table_small ts
join table_detail td on td.record_uid = ts.record_uid
There are also a number of other joins to records in other tables, but I'm not worried about appending to those ones. I'm only worried about appending to the "Small" and "Detail" tables - at the same time.
Is such a thing possible in an ADO Query? I'm willing to tweak and modify the SQL statement in any way necessary to make this possible. I have a bad feeling though that it's not possible.
Compatibility:
SQL Server 2000 through 2008 R2
Delphi XE2
Editing these Fields which have no influence on the joins is usually no problem.
Appending is ... you can limit the Append to one of the Tables by
procedure TForm.ADSBeforePost(DataSet: TDataSet);
begin
inherited;
TCustomADODataSet(DataSet).Properties['Unique Table'].Value := 'table_small';
end;
but without an Requery you won't get much further.
The better way will be setting Values by Procedure e.g. in BeforePost, Requery and Abort.
If your View would be persistent you would be able to use INSTEAD OF Triggers
Jerry,
I encountered the same problem on FireBird, and from experience I can tell you that it can be made(up to a small complexity) by using CachedUpdates . A very good resource is this one - http://podgoretsky.com/ftp/Docs/Delphi/D5/dg/11_cache.html. This article has the answers to all your questions.
I have abandoned the original idea of live ADO query updates, as it has become more complex than I can wrap my head around. The scope of the data push project has changed, and therefore this is no longer an issue for me, however still an interesting subject to know.
The new structure of the application consists of attaching multiple "Field Links" on various fields from the original set of data. Each of these links references the original field name and a SQL Statement which is to be executed when that field is being imported. Multiple field links can be on one single field, therefore can execute multiple statements, placing the value in various tables, etc. The end goal was an app which I can easily and repeatedly export a common dataset from an original source to any outside source with different data structures, without having to recompile the app.
However the concept of cached updates was not appealing to me, simply for the fact pointed out in the link in RBA's answer that data can be changed in the database in the mean-time. So I will instead integrate my own method of customizable data pushes.
So I'm not necessarily saying this is even a good idea if it were possible, since the schema of the view would be extremely volatile, but is there any way to represent a has-many relationship in a single view?
For example, let's say I have a customer that can have any number of addresses in the database. Is there any way to list out each column of each address with perhaps a number as a part of the alias (e.g., columns like Customer Id, Name, Address_Street_1, Address_Street_2, etc)?
Thanks!
Not really - you really are doing a dynamic pivot. It's possible to use OPENROWSET to get to a dynamically generated query, but whether that's advisable, it's hard to say without seeing more about the business case.
First make a stored proc which does the dynamic pivot like I did on the StackExchange Data Explorer.
Basically, you generate dynamic SQL which builds the column list. This can only really be done in a stored proc. Which is fine for applciation calls.
But what about if you want to re-use that in a lot of different joins or ad hoc queries?
Then, have a look at this article: "Using SQL Servers OPENROWSET to break the rules"
You can now call your stored proc by looping back into the server and then getting the results into a rowset - this can be in a view!
The late Ken Henderson has some good examples of this in his excellent book: "The Guru's Guide to SQL Server Stored Procedures, XML, and HTML" (you got to love the little "Covers .NET!" on the cover which captures well the zeitgeist for 2002!).
He only covers the loopback part (with views and user-defined functions), the less verbose PIVOT syntax was not available until 2005, but PIVOTs can also be generated using a CASE statement as a characteristic function.
Obviously, this technique has caveats (I can't even do this on our production server).
Yes - use:
CREATE VIEW customer_addresses AS
SELECT t.customer_id,
t.customer_name,
a1.street AS address_street_1,
a2.street AS address_street_2
FROM CUSTOMER t
LEFT JOIN ADDRESS a1 ON a1.customer_id = t.customer_id
LEFT JOIN ADDRESS a2 ON a2.customer_id = t.customer_id
If you provided more info, it'd be easier to give you a better answer. It's possible you're looking to pivot data (turn rows into columns).
Simply put, no. Not without dynamically recreating the view every time you want to use it at least, that is.
But, what you can do is predefine, say, 4 address columns in your view, then populate the first four results of your one-to-many relation into those columns. It's not quite the dynamic view you want, but it's also much more stable/usable in my opinion.
I'm using Zend Framework's Zend_Db_Table classes to fetch data from a database.
I'd like to "refine" each row I fetch from a table by adding something to it. Within a plain old SQL query I would write eg. SELECT *, dueDate<NOW() AS isOverdue. In this example, feeding an extra field to the SQL query would be possible, but sometimes it might be more suitable to do the extra stuff with PHP. Anyway, I'd use this information mainly in my views, eg. to highlight overdue items accordingly.
What would be a good place to add this isOverdue data in a ZF application?
My thoughts so far:
finding that ZF has a built-in mechanism for this (not successful so far)
subclassing Zend_Db_Table_Row
overriding _fetch() in my Zend_Db_Table class
rethinking whether this is a sane pattern at all :)
As a bonus, it would be nice that I could still use ZF to update rows. Maybe this would be (another) reason for a naming convention for custom fields?
Why reinventing the wheel? There's a built in functionality to do this:
$this->select()->from('your_table_name_here', array('*', 'dueDate<NOW() AS isOverdue'));
Simply specify what columns you need using the second parameter of from() function and it will generate the SQL that you need (by default, if you do not use a second parameter it generates "SELECT * FROM table" query).
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