I'm trying to check if a record in a table already exists.
How could I do that?
I already wrote the following code:
string dbName = "Data Source=searchindex.db";
SQLiteConnection con = new SQLiteConnection(dbName);
con.Open();
SQLiteCommand cmd = new SQLiteCommand(con);
// If this sql request return false
cmd.CommandText = "SELECT rowid FROM wordlist WHERE word='word'";
cmd.ExecuteNonQuery();
// then add record in table
cmd.CommandText = "INSERT INTO wordlist(word) VALUES ('word')";
To check if that record exists you could simplify your code
cmd.CommandText = "SELECT count(*) FROM wordlist WHERE word='word'";
int count = Convert.ToInt32(cmd.ExecuteScalar());
if(count == 0)
{
cmd.CommandText = "INSERT INTO wordlist(word) VALUES ('word')";
cmd.ExecuteNonQuery();
}
ExecuteScalar will return the first column on the first row returned by your query.
(The link is for SqlServer, but it is identical for SQLite, because the SQLiteCommand should implement the IDbCommand interface)
Another approach to use is the following
cmd.CommandText = "INSERT INTO wordlist (word)
SELECT ('word')
WHERE NOT EXISTS
(SELECT 1 FROM wordlist WHERE word = 'word');";
cmd.ExecuteNonQuery();
This is even better because you use a single query and not two (albeit the difference in a local db should be minimal)
insert into wordlist(word)
select 'foo'
where not exists ( select 1 from wordlist where word = 'foo')
If you are using sqlite-net-pcl you could write the following.
I have a base class for several tables and in it, I have a RowExists method.
The relevant source code looks as follows:
public abstract class BaseSQLiteAccess
{
protected SQLiteConnection _databaseConnection;
protected String TableName { get; set; }
//...
protected bool RowExists(int id)
{
bool exists = false;
try
{
exists = _databaseConnection.ExecuteScalar<bool>("SELECT EXISTS(SELECT 1 FROM " + TableName + " WHERE ID=?)", id);
}
catch (Exception ex)
{
//Log database error
exists = false;
}
return exists;
}
}
Related
When i run my code in the debugger and I hover my mouse over the parameters they do have the right values in them. It just doesn't update my database but when I copy the query and put it into the database it works without a problem.
The parameter values are:
id = 7
omschrijving = douche muntjes
prijs = 0,5
catagorie = faciliteiten
I checked the connection tring by using an insert query and that does add records to my database. And There is an id with the value of 7 in the database.
When I run a insert query or a delete query through my C# code it does work it's just the update statement that doesn't work. If anyone sees the issue please help me.
public static void wijzigprijs(int id, string omschrijving, decimal prijs, string catagorie)
{
try
{
try
{
OleDbConnection verbinding = new OleDbConnection(
#"Provider=Microsoft.ACE.OLEDB.12.0;
Data Source=..\..\..\La_Rustique.accdb;
Persist Security Info=False;");
verbinding.Open();
}
catch (Exception ex)
{
MessageBox.Show(ex.Message);
}
OleDbCommand query = new OleDbCommand();
query.CommandText = #"UPDATE prijslijst
SET omschrijving = #omschrijving,
prijs = #prijs,
catagorie = #catagorie
WHERE id = #id";
query.Parameters.Add(new OleDbParameter("#id", OleDbType.Integer));
query.Parameters["#id"].Value = id;
query.Parameters.Add(new OleDbParameter("#omschrijving", OleDbType.VarChar));
query.Parameters["#omschrijving"].Value = omschrijving;
query.Parameters.Add(new OleDbParameter("#prijs", OleDbType.Decimal));
query.Parameters["#prijs"].Value = prijs;
query.Parameters.Add(new OleDbParameter("#catagorie", OleDbType.VarChar));
query.Parameters["#catagorie"].Value = catagorie;
query.Connection = verbinding;
query.ExecuteNonQuery();
MessageBox.Show("succesvol gewijzigd");
}
catch (Exception ex)
{
MessageBox.Show(ex.Message);
}
finally
{
verbinding.Close();
}
}
EDIT UPDATE
Look at this topic. Here he explains how you should use variables with OleDbCommand
Variables with OleDbCommand
This is how you typically will do it when using SQLCommand parameters:
I know this doesnt answer your questions quite, but when i use SQLCommand i use this code whenever i want to update or insert with variables:
string query = #"UPDATE prijslijst
SET omschrijving = #omschrijving,
prijs = #prijs,
catagorie = #catagorie
WHERE id = #id";
SqlCommand cmd = new SqlCommand(query, connDatabase);
cmd.Parameters.Add("#id", SqlDbType.integer).Value = 7;
cmd.ExecuteNonQuery();
connDatabase.Close();
So you should be able to do the samething. Hope this will help you.
I have never seen OleDB queries written in the above syntax.
To state it differently: OleDB simply does not use named parameters, it uses the position only.
Try to change your SQL statement like this:
query.CommandText = #"UPDATE prijslijst
SET omschrijving = ?,
prijs = ?,
catagorie = ?
WHERE id = ?";
and then add the parameters in sequence of above in the code
below that.
Case: I'm trying execute a query in C# with MySql.Data.MySqlClient, which containts INSERT INTO, i'm getting an error(see below):
Database table:
What im trying to achieve: I want to insert into a new record with: "value_id(Auto Increment)", "machine_id" "tag_name", "int_value", "real_value" and "bool_value";
I have the following code:
*Retrieving machine ID
private void getMachineID()
{
string connStr = "";
string ipAdressID = "'" + machineIP + "'";
string basicQueryID = "SELECT machine_id FROM machine WHERE machine.machine_ip LIKE ";
string totalQueryID = basicQueryID + ipAdressID;
//Create connection
MySqlConnection conn = new MySqlConnection(connStr);
//Query command
MySqlCommand cmd = conn.CreateCommand();
//Assign string to query
cmd.CommandText = totalQueryID;
//Open connection
conn.Open();
//Get result ID from machine where IP adress = machineIP and write to machineID variable.
machineID = (int)(cmd.ExecuteScalar());
}
Code to insert into the record:
try
{
string connStr = "";
MySqlConnection conn = new MySqlConnection(connStr);
MySqlCommand cmd = conn.CreateCommand();
cmd.CommandText = "INSERT INTO waardes(machine_id, tag_name, int_value, real_value, bool_value) VALUES(#machineID, #tagName, #intValue, #doubleValue, #boolValue)";
cmd.Parameters.AddWithValue("#tagName", tagName);
cmd.Parameters.AddWithValue("#intValue", intValue);
cmd.Parameters.AddWithValue("#doubleValue", doubleValue);
cmd.Parameters.AddWithValue("#boolValue", boolValue);
cmd.Parameters.AddWithValue("#machineID", machineID);
conn.Open();
cmd.ExecuteNonQuery();
}
catch (Exception ex)
{
MessageBox.Show(ex.ToString());
}
Hope you guys can help!
There's no INSERT with where clause.
Take a look at this question: How to insert with where clause
Maybe, you can create an IF inside your app to verify your parameters before executing the INSERT statement.
Based on your query, I believe you need an UPDATE:
UPDATE waardes SET tag_name = #tagName,
int_value = #intValue, real_value = #doubleValue,
bool_value = #boolValue WHERE machine.machine_id LIKE %1%
Is this what you need?
you cannot use where in insert statement, because insert statement is used for adding new rows to table. you better use update statement.
There can be no Where clause used with Insert. However you can use Where when you are using Insert Into. In your statement I suppose you are missing the Select From before your Where clause.
Consider the example:
INSERT INTO tableNameDestination
SELECT feild(s),...
FROM tableNameSource
WHERE Condition
In your case:
INSERT INTO waardes(tag_name, int_value, real_value, bool_value) VALUES(#tagName, #intValue, #doubleValue, #boolValue) Select field1, field2, field3, field4 from machine WHERE machine.machine_id LIKE " + "'" + machineID + "'";
I'm using this code to select the maxID from a database table and each time I want to add a new record, the autogenerated ID is not the last one +1.
public formularAddCompanie()
{
InitializeComponent();
try
{
string cs = "Data Source=CODRINMA\\CODRINMA;Initial Catalog=TrafficManager;Integrated Security=True";
string select = "SELECT max(IDCompanie) FROM Companii";
using (SqlConnection con = new SqlConnection(cs))
{
con.Open();
SqlCommand cmd2 = new SqlCommand(select, con);
SqlDataReader sda = cmd2.ExecuteReader();
DataTable idmax = new DataTable("idmax");
idmax.Load(sda);
if (idmax.Rows[0][0].ToString().Trim() == "") { txtID.Text = "1"; }
else { txtID.Text = (int.Parse(idmax.Rows[0][0] .ToString() + 1).ToString()); }
}
}
catch (Exception er) { MessageBox.Show(er.Message); }
}
The table from where the selection is made, looks like this:
IDCompany Name Address City RegNo
1 A Street NY 123
Each time I want to add a new record, the autogenerated ID is like this: 11, 111, 1111. It takes the last ID and add another 1 next to it. What am I missing?
Interestingly, note that
string a = "The meaning of life is " + 42;
converts 42 to a string, creating the result
a == "The meaning of life is 42"
Look at this code:
(int.Parse(idmax.Rows[0][0] .ToString() + 1).ToString()); }
You are converting idmax.Rows[0][0] to a string and adding +1 to the end of the string rather than to an integer value. Try
(int.Parse(idmax.Rows[0][0].ToString()) + 1).ToString(); }
Note that idmax.Rows[0][0] should already have an integer in it (as pointed out in the comments). If that's the case, you can simplify to
(idmax.Rows[0][0] + 1).ToString(); }
idmax.Rows[0][0].ToString() + 1 produces string, not int.
You can try
txtID.Text = (Convert.ToInt32(idmax.Rows[0][0]) + 1).ToString();
I just add this because it seems that none cares about the weakness of the code posted by the poster.
First the MAX function is not reliable if you want to find the next autoincrement value that will be assigned to an ID column. Concurrency could wreak havoc with any schema that use MAX. Just suppose that another user has already retrieved the MAX for its own INSERT operation, then depending on the relative speed of the two computers you or the other user will insert a duplicate value for the IDCompany field.
The only correct way to do this common task is to use the IDENTITY property for the column IDCompany and when you need to insert a new record you should write something like this
try
{
string insert = "INSERT INTO Companii (Name,Address,City,RegNo)
VALUES(#name,#address,#city,#regno);
SELECT SCOPE_IDENTITY()";
using (SqlConnection con = new SqlConnection(cs))
using (SqlCommand cmd = new SqlCommand(insert, con))
{
con.Open();
cmd.Parameters.Add("#name", SqlDbType.NVarChar).Value = txtBoxCity.Text;
.... and on for the other parameters ....
int companyID = Convert.ToInt32(cmd.ExecuteScalar());
... work with the just added company if required
}
}
catch (Exception er)
{ MessageBox.Show(er.Message); }
SCOPE_IDENTITY will return the last identity value inserted into an identity column in the same scope and in this context scope means the connection used by your command.
In any case, if the MAX approach is still required then the code could be simplified a lot using a modified query and SqlCommand.ExecuteScalar instead of building an SqlDataReader, filling a datatable, trying to parse the result with ifs
string getMax = #"select COALESCE(MAX(IDCompany), 0) + 1 AS maxPlusOne
from Companii"
using(SqlConnection cnn = new SqlConnection(.....))
using(SqlCommand cmd = new SqlCommand(getMax, cnn))
{
cnn.Open();
int nextCompanyID = Convert.ToInt32(cmd.ExecuteScalar());
}
The COALESCE function checks the result of the MAX function and if it is NULL returns the second parameter (here 0), then just increment by 1 to get the next MAX directly from the database. ExecuteScalar will do the call returning just the maxPlusOne alias field
try this snippet:
Convert Your String into Int. String with + operator will con-cat and with int it will add numbers.
if (idmax.Rows[0][0].ToString().Trim() == "") { txtID.Text = "1"; }
else {
txtID.Text = Convert.ToString(Convert.ToInt32(idmax.Rows[0][0] .ToString())+1); }
Try This one, my id format is USR001.The code will generate auto id based on the last id inside the database. If the last id in the database is USR001, the the code will generate USR002 and put the id to the textbox
con.Open();
string sqlQuery = "SELECT TOP 1 kode_user from USERADM order by kode_user desc";
SqlCommand cmd = new SqlCommand(sqlQuery, con);
SqlDataReader dr = cmd.ExecuteReader();
while (dr.Read())
{
string input = dr["kode_user"].ToString();
string angka = input.Substring(input.Length - Math.Min(3, input.Length));
int number = Convert.ToInt32(angka);
number += 1;
string str = number.ToString("D3");
txtKodeUser.Text = "USR" + str;
}
con.Close();
i want to check valid data...
i have a table Divisi with sample data like this:
=====================
IdDivisi NamaDivisi
=====================
1 DivisiA
2 DivisiB
3 DivisiC
in my code, i get value :
string data = DivisiA;DivXXX
so, when checked, the alert will appear invalid data.
I want to get a query like this:
select NamaDivisi from Divisi where NamaDivisi IN('DivisiA','DivXXX')
and the result is null or empty or invalid.
because there are values / data 'DivXXX' is not valid on the table Divisi
But this time, when I debug, I get the query result like this:
select NamaDivisi from Divisi where NamaDivisi IN ('DivisiA;DivXXX')
===================================================
This is the full code.
private string CekValidDivisi(string data)
{
DivisiFacade div = new DivisiFacade();
string getDivisi = div.CekValidData(data);
return getDivisi;
}
public string CekValidData(string data)
{
SqlConnection Conn = DataSetting.GetSqlConnection();
SqlCommand Comm = new SqlCommand();
try
{
Conn.Open();
string sql = #"select NamaDivisi from Divisi where NamaDivisi IN('" + data + "')";
Comm = new SqlCommand(sql, Conn);
data = Convert.ToString(Comm.ExecuteScalar());
}
finally
{
Conn.Close();
Conn.Dispose();
}
return data;
}
please help me to resolve the problem in my code. thank you ...
You have multiple problems in your code, but this is not a place to teach you basics, so I'll try to stick to the topic. If you want to have a parameter like that, you have to create it like that first. I guess the data contains string with value DivisiA;DivXXX (and I presume DivXXX is just a generic name meaning you have multiple divisions there). Probably the easiest way would be to do something like this with it
public string CekValidData(string data)
{
SqlConnection Conn = DataSetting.GetSqlConnection();
SqlCommand Comm = new SqlCommand();
try
{
Conn.Open();
string paramData = ParseData(data);
string sql = #"select NamaDivisi from Divisi where NamaDivisi IN('" + paramData + "')";
Comm = new SqlCommand(sql, Conn);
data = Convert.ToString(Comm.ExecuteScalar());
}
finally
{
Conn.Close();
Conn.Dispose();
}
return data;
}
private string ParseData(string data)
{
return data.Replace(";", "','");
}
Haven't tried it, but hope you get the idea. Either way, please for your own sake, do some research on what is the best way to handle sql connections in c# and also how to prevent SQL injections.
I have a method like this
private string AccountCreation()
{
string accountId="";
using (SqlConnection connection = new SqlConnection(ConnectionString))
{
connection.Open();
SqlCommand command = new SqlCommand();
command.Connection = connection;
StringBuilder sql = new StringBuilder();
sql.AppendLine("SELECT ACCOUNT_ID,CUSTOMER_ID FROM T_ACCOUNT order by ACCOUNT_ID desc");
sql.AppendLine("SET IDENTITY_INSERT T_ACCOUNT ON");
sql.AppendLine("INSERT INTO T_ACCOUNT (ACCOUNT_ID,CUSTOMER_ID)");
sql.AppendLine("SELECT ACCOUNT_ID + 1, CUSTOMER_ID +1 FROM T_ACCOUNT Where ACCOUNT_ID = (select max(ACCOUNT_ID) from T_ACCOUNT)");
sql.AppendLine("SET IDENTITY_INSERT T_ACCOUNT OFF");
accountId = Convert.ToString(sql.AppendLine("SELECT top 1 ACCOUNT_ID FROM T_ACCOUNT order by ACCOUNT_ID desc"));
string strUpdateQuery = sql.ToString();
ExecuteQuery(strUpdateQuery, command);
}
return accountId;
}
Now accountId is holding the query but not the value returned after execution of the query. I want the value in that string. Can anyone help me?
For getting value from the query. you need ExecuteScalar method.
object oRetVal = command.ExecuteScalar();
string accountId = string.Empty;
if(oRetVal != null)
{
accountId = oRetVal.ToString();
}
However, it is recommend to use store procedure.
I assume you are looking for the "TOP 1 Account_ID" from the query. What you have done there will not work (or give you what you want). You will need to either send in a output parameter to put the accountID in, or run fetch the data using datareader or dataset.
You'll have to bind the output of your ExecuteQuery to an object.
check if this returns any result and populates the accID.
var accID = ExecuteQuery(strUpdateQuery, command)
public string ExecuteQuery(string query,SqlCommand cmd)
{
cmd.CommandType = CommandType.Text;
cmd.CommandText = query;
object i=cmd.ExecuteScalar();
return i.ToString();
}
After this just assign this to the accounted
accountId = ExecuteQuery(strUpdateQuery, command);