I am very new to DB application development, though I have a fair amount of experience in VB.NET and C++ (self-taught, somewhat intermediate). I have a query in a table adapter with two parameters (user input) that always returns only one row from a table, based on those two parameters. Let's say row X with A, B and C columns. Filters are set on A and B in my query, but it selects all fields.
Now, I want to show the value of C in one of my main Form objects (let's say a Label in this example), but I cannot seem to be able to extract it. I know it probably is very easy, but I am a bit lost in DB code jungle..
[EDIT]
My apologies, the code bit (example).
Query:
SELECT Column1, Column2, Column3
FROM Table1
WHERE (Column1 = #Parameter1) AND (Column2 = #Parameter2)
In my VB project:
Dim temp
temp=Me.Table1TableAdapter.queryName(Me.MyProjectDBDataSet.Table1,userinput1, userinput2)
Up to this point everything works perfectly, but this is also where I get stuck. How do I, let's say, assign the value of Column3 (after running the query the result will always be only one row from Table1) to Label.Text for instance?
I hope this makes it a bit clearer..
Dim db As Database = DatabaseFactory.CreateDatabase
Dim cmd As DbCommand = db.GetSqlStringCommand(query) 'Query is a string containing your SQL command'
Dim sqlDataReader As IDataReader = db.ExecuteReader(cmd)
Dim myObj As New MyObject
If sqlDataReader IsNot Nothing Then
'Loop through the rows of the DataReader'
Do While sqlDataReader.Read()
'Do something here with the value in Column3'
myObj.myIntegerProperty= CInt(IIf(IsDBNull(.Item("Column3")), 0, .Item("Column3")))
Loop
End If
Related
Using VS 2013 (VB) and SQL server 2016.
I have linQ query that returns two columns from a database. The query is as follows.
Dim val = (From value In db.ngc_flowTypes
Where value.defaultValue IsNot Nothing
Select value.flowName, value.defaultValue)
The data it returns is a as follows.
I want to iterate through each row of the results and pass the values to certain variables. A ForEach statement doesnt seem to work as it just runs through once. I am sure this must be easy but I ont quite understand it. Am I getting the data returned in the best way via my query? Can I transpose the data to a data table in VB? so I can work with it easier?
The end result I want is string for each flow name with its corresponding default value (along with some other text). So something like this.
dim strsubmission as string = flowName + " has a value of " + defaultValue
Use ToDictionary.
Dim val = (From value In db.ngc_flowTypes
Where value.defaultValue IsNot Nothing
Select value).ToDictionary(Function(key) key.flowName,
Function(value) value.defaultValue)
This will actually execute the SQL of the linq on the database (approx. Select * From ngc_flowTypes Where defaultValue Is Not NULL), traverse each record into a key/value pair (flowName, defaultValue) and put it into a in-memory dictionary variable (val).
After that you can do whatever you like with the dictionary.
For Each flowName In val.Keys
Console.WriteLine("{0} has a value of {1}", flowName, val(flowName))
Next
Edit:
This will only work as long flowName is unique in table ngc_flowTypes
I have couple insert queries which are merged in transaction. First of that insert is to create new product articel number incrementing the most higher in table by one. Unfortunetly i just noticed that mostly during tests if for instance two users from two diffrent applications click button which trigger my transaction's method they could get same new product number. How can avoid that situation? Is there something like lock on first insertion so that if first user accessing table to insert restrict other's user/s about their insertion so they have to wait in queue after first user insert is finished? Is there something like that? Besides i thought if someone inserts other users are not able to insert. I made comments in code you to understand.
Part of my transaction query below:
Public Sub ProcessArticle(ByRef artikel As ArticlesVariations)
Dim strcon = New AppSettingsReader().GetValue("ConnectionString", GetType(System.String)).ToString()
Using connection As New SqlConnection(strcon)
connection.Open()
Using transaction = connection.BeginTransaction()
Try
For Each kvp As KeyValuePair(Of Integer, Artikel) In artikel.collection
articleIndex = kvp.Key
Dim art As Artikel = kvp.Value
Using cmd As New SqlCommand("INSERT INTO tbArtikel (Nummer) VALUES (#Nummer);Select Scope_Identity()", transaction.Connection)
cmd.CommandType = CommandType.Text
cmd.Connection = connection
cmd.Transaction = transaction
'Get next product number from table tbArtikel (this will be new product number)'
Dim NewArtNummer as String = New DALArtikel().GetNewArtikelNumber(transaction)
art.Nummer = NewArtNummer
cmd.Parameters.AddWithValue("#Nummer", art.Nummer)
'Get inserted product id for other diffrent inserts below'
newArticleRowId = CInt(cmd.ExecuteScalar())
'....
other INSERTs queries to other tables ...
...'
transaction.Commit()
Catch ex As Exception
transaction.Rollback()
Throw 'Rethrow exception.'
End Try
End Using
End Using
End Sub
Just about the only way to assure that users are not assigned the same values is to issue them from the server when the row is inserted. It is the entire premise behind the server issuing AI values for PKs.
BUT since your thing is a multi-segment, "numeric string" that presents a problem. Rather than tearing the string apart to find the Max()+1 for one segment with a WHERE clause on parts of the string. Consider something like this:
Start with a table used to increment and issue the values:
{DocId Int, SegmentB int, SegmentC Int}
This will simply track the values to use in the other table. Then a stored procedure to create/increment a new code (MySQL - this is a conceptual answer):
CREATE DEFINER=`root`#`localhost` PROCEDURE `GetNextProductCode`(in docId int,
in Minr int,
in Rev int
)
BEGIN
SET #maxR = 0;
SET #retCode ='';
if Minr =-1 then
Start transaction;
SET #maxR = (SELECT Max(SegmentB) FROM articlecode WHERE MainId = docId) + 1;
UPDATE articlecode SET SegmentB = #maxR WHERE MainId = docId;
Commit;
Select concat(Cast(docId As char) , '.',
Cast(#maxR AS char) , '.',
Cast(Rev As char)
);
end if;
END
This is a rough idea of the process. As such, it only works on the second segment (I dunno what happens when you create a NEW SegmentB - does SegmentC reset to 1???). The idea is:
pass numbers so there is no need to tear up a string
pass -1 for the segment you need the next value for
the sp gets the Max()+1 and updates the counter table so the next user will get a new value
If for some reason you end up not saving the row, there will be gaps
the sp uses a transaction (probably only needs to protect the update) so that only 1 update can happen at a time
returns the new code. it could just return 2 values, but your going to glue them together anyway
There is much To Do:
It only does SegmentB
For a NEW DocId (-1), insert a new row with 1000 and 1(?) defaults
Same for a NEW segmentB (whatever it is): insert a new row for that DocId with default values
To get a new code before you insert a row:
cmd.CommandType = CommandType.StoredProcedure
cmd.Parameters.Add("docId", MySqlDbType.Int32).Value = 3
cmd.Parameters.Add("Minr", MySqlDbType.Int32).Value = -1
cmd.Parameters.Add("Rev", MySqlDbType.Int32).Value = 1
dbcon.Open()
Using rdr = cmd.ExecuteReader()
rdr.Read()
Console.WriteLine(rdr(0))
End Using
The obvious downside is that each insert requires you to hit the DB in order to...well save to the DB. If they were int values it could be a Trigger.
I'm a SQL developer and my VB skills are about fifteen years out of date, but instead of creating the incremented number yourself in VB just let SQL generate them with an IDENTITY field. SQL will never allow duplicates and then you just need to return the SCOPE_IDENTITY():
ALTER TABLE dbo.tbArtikel
ADD [ArtikelID] INT IDENTITY(1,1) PRIMARY KEY;
I have two suggestions:
First suggestion: move your code to a stored procedure this way all your users will execute the same transaction where you can set your isolation level the way you want. Read This.
Second suggestion: I would create a unique index on your field Nummer. This way when I try to insert a duplicate value it will raise an error that I can deal with it by telling the user that he need to retry the same operation or retry it automatically.
Trying to lock the record or the table for your operation is not advisable, however you can check this article on code project you might find what you are looking for. Make sure that you provide a mechanism of releasing all locks if your program stops at the middle of the transaction.
I am creating a winform application in c#.and using sql database.
I have one table, employee_master, which has columns like Id, name, address and phone no. Id is auto increment and all other datatypes are varchar.
I am using this code to get the next auto increment value:
string s = "select max(id) as Id from Employee_Master";
SqlCommand cmd = new SqlCommand(s, obj.con);
SqlDataReader dr = cmd.ExecuteReader();
dr.Read();
int i = Convert.ToInt16(dr["Id"].ToString());
txtId.Text = (i + 1).ToString();
I am displaying on a textBox.
But when last row from table is deleted, still I get that value which is recently deleted in textbox
How should I get the next autoincrement value?
To get the next auto-increment value from SQLServer :
This will fetch the present auto-increment value.
SELECT IDENT_CURRENT('table_name');
Next auto-increment value.
SELECT IDENT_CURRENT('table_name')+1;
------> This will work even if you add a row and then delete it because IDENT_CURRENT returns the last identity value generated for a specific table in any session and any scope.
try this:
SELECT IDENT_CURRENT('tbl_name') + IDENT_INCR('tbl_name');
If you are using Microsoft SQL Server. Use this statement to get current identity value of table. Then add your seed value which you have specified at time of designing table if you want to get next id.
SELECT IDENT_CURRENT(<TableName>)
As for me, the best answer is:
dbcc checkident(table_name)
You will see two values (probably same)
current identity value , current column value
When you delete a row from the table the next number will stay the same as it doesnt decrement in any way.
So if you have 100 rows and you deleted row 100. You would have 99 rows but the next number is still going to be 101.
select isnull((max(AddressID)+1),1) from AddressDetails
the max(id) will get you maximum number in the list pf employee_master
e.g. id = 10, 20, 100 so max will get you 100
But when you delete the record it must have been not 100
So you still get 100 back
One important reason for me to say this might be the issue because you are not using order by id in your query
For MS SQL 2005 and greater:
Select Cast(IsNULL(last_value,seed_value) As Int) + Cast(increment_value As Int) As NextID
From sys.identity_columns
WHERE NAME = <Table_Name>
Just a thought, if what you wanted was the last auto-number that you inserted on an already open connection try using:
SELECT ##IDENTITY FROM...
from that connection. That's the best way to keep track of what has just happened on a given connection and avoids race conditions w/ other connections. Getting the maximum identity is not generally feasible.
SqlConnection con = new SqlConnection("Data Source=.\SQLEXPRESS;Initial Catalog=databasename;User ID=sa;Password=123");
con.Open();
SqlCommand cmd = new SqlCommand("SELECT TOP(1) UID FROM InvoiceDetails ORDER BY 1 DESC", con);
SqlDataReader reader = cmd.ExecuteReader();
//won't need a while since it will only retrieve one row
while (reader.Read())
{
string data = reader["UID"].ToString();
//txtuniqueno.Text = data;
//here is your data
//cal();
//txtuniqueno.Text = data.ToString();
int i = Int32.Parse(data);
i++;
txtuid.Text = i.ToString();
}
Which one could be a better practice? In my situation, I need to check if a specific data exists in a table. I am iterating through an Excel file and verifying if a code there exists in my table using VB.NET. I have two options to do this (or if there is a better way to do this, I am open for suggestions).
First is to check it one by one, this code is executed per loop:
SQL = "SELECT TOP 1 * FROM Table1 WHERE Code = '" & codeFromExcel & "'"
rs = dbConn.Execute(SQL)
If Not rs.EOF Then
isFound = True
Else
isFound = False
End If
The other one is I load all the codes in a List(Of T)
Dim myList As New List(Of String)()
rs = Nothing
rs = dbConn.Execute("Select Code from Table1")
If Not rs.EOF Then
Do While Not rs.EOF
myList.Add(rs.Fields("Code").Value.ToString)
rs.MoveNext()
Loop
End If
Then check every record if it is in the List(Of T) while iterating in the Excel.
If myList.Contains(codeFromExcel) Then
isFound = True
Else
isFound = False
End If
I've been working with this kind of stuff most of the time and I want to know which one is the most efficient way to use. At the moment I only have a few records in my database. I want my code to be ready and efficient when the time comes that I need to deal with numerous records. Thanks in advance!
Additional info: The data doesn't need to be "fresh" as that table is meant for one-time entry only.
Personally I prefer to open as less connections to data base as possible.
So:
If the table is not very large (some hundred rows) I would go with the "cache" option.
Generally:
I would gather all excel codes in a list. ( excelCodes )
Then I would query something like Select Distinct Code from Table1 Where Code In ( excelCodesList ) and store it in a second list ( foundCodes ).
Then I would compare these lists.
I test it on a table with 6.143.993 rows.
To select just one column (description) to "cache" took 1'29".
On the other hand query like:
select distinct description from ItemDetail where description in ( 'abc','cddd','xxx' )
took 0'58".
UPDATE
An index on Code column might help with performance.
My query in SQL Server is sorted by several factors, and when I execute it the ordering is all correct. I have some subforms that are populated using the following code:
Set db = OpenDatabase("", False, False, globalstrSQLConnection)
strSQL = "SELECT * FROM qryTaskSimple"
Set rs = db.OpenRecordset(strSQL, dbOpenSnapshot, dbSeeChanges)
Set Me.Recordset = rs
where globalstrSQLConnection is the connection to the database on my my SQL Server and qryTaskSimple is the query mentioned above. But the subforms are sorted by a completely different criterion. Instead of being sorted by:
ORDER BY CASE WHEN tblTask.JobNum LIKE '***FULL***' THEN 0 ELSE 1 END, DivisionSortID, SuperintendentSortID, ISNULL(dbo.tblTask.Ordering, 999999999),
dbo.tblTask.JobNum, dbo.tblTask.Sequence
as stated inside the query, it seems to be sorted by only tblTask.JobNum... even when I replace the entire ORDER BY clause with ORDER BY DivisionSortID... And I don't have any VBA code that further sorts the subforms.
Queries and tables in Access have an underlying query/table object order by that can over-ride the SQL order by. You can see it (and remove it) in respective object properties.
It can be pretty frustrating and I'm not really sure if that's what's going on, but regardless, you can force desired sorting by simply adding it to your SQL statement, treating the query as a table.
strSQL = "SELECT * FROM qryTaskSimple ORDER BY <your desired sorting using any qryTaskSimple cols>"
if that doesn't work, then try the (sub)forms orderby at the form's load() event:
Private Sub Form_Load()
me.orderby = "your order by statements"
if me.orderbyon = false then me.orderbyon = true
End Sub