I have a problem - I want to get value from my SQL Server select but it returns:
System.Data.SqlClient.SqlDataReader
Code:
static SqlConnection sqlconnection = new SqlConnection("Data Source=XXXX;Initial Catalog=XXXX;Integrated Security=True");
static SqlCommand sqlcommand = new SqlCommand("SELECT * FROM XXX where XXX = 'XXXX'", sqlconnection);
public static string DBSQL()
{
// connect to database
sqlconnection.Open();
// execute
SqlDataReader myReader = sqlcommand.ExecuteReader();
// return valueAC
return myReader.ToString();
}
You missed a few steps. Always consult the examples provided by the vendor. In particular you're trying to return the reader itself, but instead you need to read data from it. Something like this:
SqlDataReader myReader = sqlcommand.ExecuteReader();
try
{
if (myReader.HasRows)
{
// What should you do if there's more than one row?
while (myReader.Read())
{
// Which value are you trying to read?
return myReader.GetString(0);
}
}
else
{
// What do you do when no rows are found?
return string.Empty;
}
}
finally
{
// Make sure to close the reader
myReader.Close();
}
Note a few questions in the code comments that are really up to you to answer:
You're selecting potentially zero-to-many records, but trying to return a single value. What do you want/expect to happen when the result count is anything other than 1?
You're doing a SELECT *, which is presumably getting more than one value from the database. Which value are you looking to return? (And why select more than that one?)
You can decide what to do in those various cases. But ultimately when using a DataReader you need to fetch the rows returned.
Related
Hello everyone I am currently working on some testing project and I am having a little problem. Using selenium, I need to SendKey in specific element but instead of fixed value i need to use value (data) from my database. Can anyone help me with how to retrieve single value from database and store it in a variable so i can use it later.
Thank you and sorry for a noobish question - see code below:
SqlConnection conn = new SqlConnection();
SqlCommand command;
SqlDataReader dataReader;
conn.ConnectionString = "Server=******;Database=****;User ID=sqlserver;password=****;MultipleActiveResultSets=true;");
string query = "select RequestID, from AutomaticPayment where RequestID ='1230322'";
DataTable dt = new DataTable();
command = new SqlCommand(query, conn);
conn.Open();
dataReader = command.ExecuteReader();
dt.Load(dataReader);
driver.FindElement(By.Id("requestID")).SendKeys(VALUE FROM DATABASE);
You can use the following code
using (SqlConnection connection = new SqlConnection(_connectionString))
{
SqlDataAdapter sda = new SqlDataAdapter(query, connection);
connection.Open();
SqlCommand cmd = new SqlCommand(query, connection);
try
{
result = cmd.ExecuteScalar().ToString();
}
catch(NullReferenceException n)
{
result = "";
}
}
ExecuteScaler gets you the first column of the first row and additional columns are ignored. Use the value from result in your SendKeys()
Use conditions to limit the result:
Select data
SELECT TOP 1 RequestID FROM AutomaticPayment // Always returns 1 row
Or
SELECT RequestID FROM AutomaticPayment WHERE Id = 123 // Id must be unique to return 1 row
And maybe other ways.
Get value
var value = dt.Rows[0][1];
Or
var value = dt.Rows[0]["RequestID"];
From what i worked on with SqlCommand just do the following :
int yourId = 0;
dataReader = command.ExecuteReader()
while(dataReader.Read())
{
yourId = dataReader.GetInt32(0);
}
With that, you should have your value set to the first column of the dataReader. (that is selected thanks to your query, since you are requesting on a specific id, i guess it will return only one column
there is many other type available for Reader : Reader Microsoft Doc
And if you have in the futur many data to collect, use the ORM entity framework, work well for me
Source
EDIT :
Since you are only querying one data, maybe the solution of #work_ishaan is better than mine in this case, check it out.
So i have a class Take for connecting to mysql. In that class I have a method to call a query to take the last record from mysql table.
public void Balance()
{
string query = "SELECT balance FROM history ORDER BY id DESC LIMIT 1 ";
if (this.OpenConnection() == true)
{
MySqlCommand cmd = new MySqlCommand(query, connection);
cmd.ExecuteNonQuery();
}
}
In the main form I'm calling that class and that method
take.Balance();
I know, that from code above, i don't get any value but NULL, so i am asking how i can take value from that query and put it in the TextBox in the main form?
Personally, I think you should improve your basic knowledge of programming. There are two big problems in your example code:
You want to get the value, but your function is void, not return anything even set the value to some variable
ExecuteNonQuery is not your case.
For example:
public string Balance()
{
string query = "SELECT balance FROM history ORDER BY id DESC LIMIT 1 ";
if (this.OpenConnection() == true)
{
MySqlCommand cmd = new MySqlCommand(query, connection);
return cmd.ExecuteScalar();
}
}
Let's have look:
// You probably want to return value: decimal, not void
public decimal Balance() {
// Make sql readable
string query =
#"SELECT balance
FROM history
ORDER BY id DESC
LIMIT 1 ";
// do not cache connection, but create a new one instead
using (MySqlConnection conn = new MySqlConnection(connectionStringHere)) {
conn.Open();
// wrap IDisposable into using
using (MySqlCommand cmd = new MySqlCommand(query, conn)) {
// you want to return values: ExecuteReader (or ExecuteScalar)
// instead of ExecuteNonQuery
using (var reader = cmd.ExecuteReader()) {
if (reader.Read())
return Convert.ToDecimal(reader.GetValue(0));
else
return 0m; // cursor is empty, let's return 0
}
}
}
}
There are two things to consider. First, the query
"SELECT balance FROM history ORDER BY id DESC LIMIT 1"
is a query in the sense that some useful data from the database should be returned, it should not be executed with a the method ExecuteNonQuery, which is intended to return the number of rows affected by a non-query statement. Second, the return type of Balance would have to be changed to some other type than void, say int or something similar, which would have to be returned to the caller.
Hi I am trying to create CRUD functions in C# but am stuck on my first one which is FetchALL, as so far it says not all code path returns a value.
Heres my code so far
public SqlDataReader FetchAll(string tableName)
{
using (SqlConnection conn = new SqlConnection(_ConnectionString,))
{
string query = "SELECT * FROM " + tableName;
SqlCommand command = new SqlCommand(query, conn);
using (SqlDataReader reader = command.ExecuteReader())
conn.Open();
conn.Close();
}
}
}
}
I can give you more information, thanks
You have a return type of SqlDataReader, but you aren't returning anything anywhere in your code. At the very least you should declare your data reader and return it like this:
public SqlDataReader FetchAll(string tableName)
{
SqlDataReader reader;
using (SqlConnection conn = new SqlConnection(_ConnectionString))
{
string query = "SELECT * FROM " + tableName;
// added using block for your command (thanks for pointing that out Alex K.)
using (SqlCommand command = new SqlCommand(query, conn))
{
conn.Open(); // <-- moved this ABOVE the execute line.
reader = command.ExecuteReader(); // <-- using the reader declared above.
//conn.Close(); <-- not needed. using block handles this for you.
}
}
return reader;
}
Note, I've noted a few other problems I saw as well, which you can see by my comments.
Also, I want to point out something very important: you should always avoid string concatenation in queries as this opens you up to the risk of a SQL injection attack (as gmiley has duly pointed out). In this case, you should create an enum which contains values associated with all the possible table names, and then use a dictionary to look up the table names based on their enum values. If a user provides an invalid/unknown value, you would then thrown an argument exception.
This isn't the end of your problems, though (as Default has pointed out). You can't create the connection in a using block, which disposes and closes as soon as it exits the block, and then use the SqlDataReader that is returned from the method. If I were you, I'd return a DataSet instead of a SqlDataReader. Here's how I'd do it:
First, create your enum of possible table values:
public enum Table
{
FirstTable,
SecondTable
}
And a dictionary that maps table enum values to the table names (which you will populate in your static constructor):
private static Dictionary<Table, string> _tableNames = new Dictionary<Table, string>(); // populate this in your static constructor.
And then here is your method to fetch the data:
public static System.Data.DataSet FetchAll(Table fromTable)
{
var ret = new System.Data.DataSet();
using (var conn = new System.Data.SqlClient.SqlConnection(_connectionString))
{
string tableName = "";
if (!_tableNames.TryGetValue(fromTable, out tableName)) throw new ArgumentException(string.Format(#"The table value ""{0}"" is not known.", fromTable.ToString()));
string query = string.Format("SELECT * FROM {0}", tableName);
using (var command = new System.Data.SqlClient.SqlCommand(query, conn))
{
using (var adapter = new System.Data.SqlClient.SqlDataAdapter(command))
{
adapter.Fill(ret);
}
}
}
return ret;
}
One final note, I'd advise you name your class-level variables with lower camel case per convention, e.g. _connectionString.
Firstly you aren't returning anything from the method. I'd add, are you sure you want to return a SqlDataReader? It is declared within a using block, so it will be closed by the time you return it anyway. I think you should re-evaluate what this function should return.
You need a return statment for the method to return a value.
I have a Winforms that is connecting to a SQL Server 2008 database.
I would like to be able to easily filter through data in one table.
Here is an example of what I would like:
there are 3 columns in the table, and I will have three textboxes (or any other useful control) on a form that will correspond to those three columns.
the user will be able to input a value in any one of those fields and retrieve the rest of the values pertaining to that field.
Is there already an easy solution for this?
Yes you can use DataSet or DataReader.
http://msdn.microsoft.com/en-us/library/ms171897%28v=vs.80%29.aspx
http://www.dotnetperls.com/datagridview-tutorial
I don't think there is a yet unique way of doing this. Anyways, you can simply use a SqlCommand it will allow you to execute a storedprocedure or a query as you like. The you pass the three filter values as SqlParameters.
Here is a little example:
private static void ReadOrderData(string connectionString)
{
string queryString =
"SELECT * FROM MyTable Where (FieldOne == #ParameterOne Or FieldTwo = #ParameterTwo Or FieldThree = #ParameterThree)";
using (SqlConnection connection = new SqlConnection(
connectionString))
{
// Create the command
SqlCommand command = new SqlCommand(
queryString, connection);
// Add the parameters
command.Parameters.Add(new SqlParameter("ParameterOne", txtMyTextBox1.Text));
command.Parameters.Add(new SqlParameter("ParameterTwo", txtMyTextBox2.Text));
command.Parameters.Add(new SqlParameter("ParameterThree", txtMyTextBox3.Text));
connection.Open();
SqlDataReader reader = command.ExecuteReader();
try
{
while (reader.Read())
{
Console.WriteLine(String.Format("{0}, {1}",
reader[0], reader[1]));
}
}
finally
{
// Always call Close when done reading.
reader.Close();
}
}
}
Then you use the SqlDataReader to get the values.
The following code does not work. There is only 1 row in this table. How do I just get the statement that the sql would return?:
SqlConnection conn = new SqlConnection(connectionStringArg);
SqlCommand command = new SqlCommand("select applicationname from tbl_settings");
command.Connection = conn;
conn.Open();
string simpleValue = command.ExecuteReader()[0].ToString();
conn.Close();
return simpleValue;
Okay any help on how to achieve this relatively simple task would be great.
Since there's only a single value returned, you could do this:
string value = (string)command.ExecuteScalar();
If you need more than the first column from the first row returned, you'll need to use ExecuteReader(). See driis' answer.
The DataReader can't be indexed like that. You need something like:
using(conn)
using(var reader = command.ExecuteReader())
{
reader.Read();
string simpleValue = reader.GetString(0);
}
The general idea is to advance the reader for each record (using Read), then you can read values from the row. As pointed out in another answer, if you know there is only one single value in the result set, command.ExecuteScalar() gives you just that.
You have to call the Read method on a DataReader returned from ExecuteReader to get to the first row. Something like this:
SqlDataReader rdr = command.ExecuteReader();
if (rdr.Read())
...
You'd do e.g.
using(SqlConnection conn = new SqlConnection(connectionStringArg))
using(SqlCommand command = new SqlCommand("select applicationname from tbl_settings")) {
command.Connection = conn;
conn.Open();
SqlDataReader reader = command.ExecuteReader();
if(reader.read()) {
return reader.GetString(0);
}
return null;
}
For a single string you want to use ExecuteScalar to get a single value and then attempt to cast it to string.
From doc: Executes the query, and returns the first column of the first row in the result set returned by the query. Additional columns or rows are ignored.
Example:
string result = command.ExecuteScalar() as string;
For small stuff I often find LINQ2SQL the easiest to set up and use. This tutorial should get you up and running in a few minutes. For bigger projects LINQ2SQL is considered obsolete, see this question for discussion and alternatives.
Check DataReader.Read() you need to call it.
string applicationname = "";
using(var reader = command.ExecuteReader())
{
reader.Read();
applicationname = reader.GetString(reader.GetOrdinal("applicationname"));
}
var query_result = com.ExecuteScalar() as string;
if (!string.IsNullOrEmpty(query_result )) // do your thing here...