Develop Reference

How to check if a song exists?

I can Insert, Update, Delete and Search the MySql Database
I wish to know how to check if a Song Exists in MySql DataBase ...
void CheckIfFileExists(String file, String dir)
{
// $mysqli = new mysqli(SERVER, DBUSER, DBPASS, DATABASE);
string song = Path.GetFileName(file);
song = MySql.Data.MySqlClient.MySqlHelper.DoubleQuoteString(song);
string ConString = " datasource = localhost; port = *;
username = ***; password = *****";
string sql = "SELECT id FROM music WHERE song = " + song);
using (MySqlConnection cn = new MySqlConnection(ConString))
{
cn.Open();
using (MySqlCommand cmd = new MySqlCommand(sql, cn))
{
//if id exixts?
if (???????????)
{
// "Song exists";
}
else
{
// "Song does not exist";
InsertIntoDataBase(String file, String dir);
}
}
}
}

I'll go straight to the real issue, how to upsert correctly, before the question gets closed. Use MySQL's custom INSERT IGNORE and parameterized queries. Using Dapper makes this a one-liner:
var sql=#"INSERT IGNORE INTO music
(ID,song,folder)
VALUES (1, #song,#folder)";
using (var cn= new MySqlConnection(ConString))
{
cn.Execute(sql,new {song=song,folder=#dir});
}
Dapper will open the connection to execute the command and close it afterwards. It will generate a MySqlCommand, generate parameters for every property in the supplied object (#song for song, #folder for folder).
INSERT IGNORE will try to insert a new row to the table. If a row with the same primary key already exists, the INSERT will be ignored.
Generating SQL strings by concatenating input is very dangerous. No amount of quoting can prevent SQL injection attacks, or more benign conversion errors. What would happen if the song was named '0'; DROP TABLE music;-- ? What if the value was a date or number? The query string would end up with invalid characters.
Parameterized queries on the other hand are like C# functions. The parameters are passed to the server outside the string itself, as part of the RPC call. The server generates an execution plan from the query and feeds the parameter values to the compiled execution plan.
The values never change to text or get combined with the query, so there's no way to inject SQL or end up with type conversion issues

Properly check if a record already exists in a database

I have read other questions on this, but it does not help for the most part.
Trying to check if a file has already been uploaded(filename is sent to this table) before creating another record and allowing them to upload the same file again.
I am using this code and it keeps telling me every file is a new file, even when I use the same file for testing. Obviously it should result in "Exists". Connection is already established using "this.Master.Conn" so please no SQLCommand stuff.
I even tried using wildcards in the query.
private string SQLCheck(string FileName)
{
string Check = "Select VideoURL from TrainingVideo2 where VideoURL Like '" + FileName +"' and Status=1;";
Object ob = this.Master.Conn.ExecuteSqlScalarCommand(Check);
string Result;
if (DBNull.Value.Equals(ob))
{
Result = "Exists";
}
else
{
Result = "NewFile";
}
return Result;
}
Also, does anybody have a better(more efficient) way of doing this?
Trying to basically rewrite this in c#.
Private Function CheckName(name As String) As Int32
Dim sql As String = "SELECT ID FROM Company Where Name Like '" & name & "' "
Dim ob As Object = Conn.ExecuteSqlScalarCommand(sql)
If IsDBNull(ob) Then
Return 0
Else
Return CInt(ob)
End If
End Function

There are new and more innovative methods devised to get around the simple "replace all ` and " characters with ..." SQL injection prevention techniques. In your case, if the VideoURL happens to be a varchar (and not nvarchar), then using unicode character U+02BC (URL encoded = %CA%BC) would pass in a quote character as a unicode string, which would bypass your C# checks, but SQL Server will conveniently convert to a quote character in your query. This is just one example of why you should not be doing this :).
In terms of you check, I always prefer using TOP 1 to let SQL Server cut a potential table scan short. So, I would use this query:
Select TOP 1 SomeNonNullIntColumn from TrainingVideo2 where VideoURL Like ... and Status=1;
Execute the query with ExecuteScalar. If the result is null, then the record does not exist.

Never build up an SQL string like that. See SQL injection.
Why are you using like? Do you really have Sql wildcards in that fileName?
Example (sorry for the "SqlCommand stuff", but it's important):
string sql = "select count(*) from TrainingVideo2 where VideoURL = #Name and Status=1"
using (SqlConnection conn = new SqlConnection(connString))
{
SqlCommand cmd = new SqlCommand(sql, conn);
cmd.Parameters.Add("#Name", fileName);
conn.Open();
return (Int32)cmd.ExecuteScalar() > 0;
}

Checking and Saving/Loading from MySQL C#

I am making something that requires MySQL. I have the saving done from in-game, which is simply done by INSERT.
I have a column that will have a password in and I need to check if the inputted password matched any of the rows and then if it is, get all of the contents of the row then save it to variables.
Does anyone have an idea how to do this in C#?
//////////////////////////
I have found how to save and get the string, however it will only get 1 string at a time :(
MySql.Data.MySqlClient.MySqlCommand command = conn.CreateCommand();
command.CommandText = "SELECT * FROM (player) WHERE (pass)";
command.ExecuteNonQuery();
command.CommandType = System.Data.CommandType.Text;
MySql.Data.MySqlClient.MySqlDataReader reader = command.ExecuteReader();
reader.Read();
ayy = reader.GetString(1);
print (ayy);
if(ayy == password){
//something
}

My best practice is to use MySQLDataAdapter to fill a DataTable. You can then iterate through the rows and try to match the password.
Something like this;
DataTable dt = new DataTable();
using(MySQLDataAdapter adapter = new MySQLDataAdaper(query, connection))
{
adapter.Fill(dt);
}
foreach(DataRow row in dt.Rows)
{
//Supposing you stored your password in a stringfield in your database
if((row.Field<String>("columnName").Equals("password"))
{
//Do something with it
}
}
I hope this compiles since I typed this from my phone. You can find a nice explanation and example here.
However, if you are needing data from a specific user, why not specificly ask it from the database? Your query would be like;
SELECT * FROM usercolumn WHERE user_id = input_id AND pass = input_pass
Since I suppose every user is unique, you will now get the data from the specific user, meaning you should not have to check for passwords anymore.

For the SQL statement, you should be able to search your database as follows and get only the entry you need back from it.
"SELECT * FROM table_name WHERE column_name LIKE input_string"
If input_string contains any of the special characters for SQL string comparison (% and _, I believe) you'll just have to escape them which can be done quite simply with regex. As I said in the comments, it's been a while since I've done SQL, but there's plenty of resources online for perfecting that query.
This should then return the entire row, and if I'm thinking correctly you should be able to then put the entire row into an array of objects all at once, or simply read them string by string and convert to values as needed using one of the Convert methods, as found here: http://msdn.microsoft.com/en-us/library/system.convert(v=vs.110).aspx
Edit as per Prix's comment: Data entered into the MySQL table should not need conversion.
Example to get an integer:
string x = [...];
[...]
var y = Convert.ToInt32(x);
If you're able to get them into object arrays, that works as well.
object[] obj = [...];
[...]
var x0 = Convert.To[...](obj[0]);
var x1 = Convert.To[...](obj[1]);
Etcetera.

How to Modify FoxPro memo in C#?

I have a very big string to be updated to the memo field of FoxPro Table, I tried
cmd = db.GetSqlStringCommandWrapper("UPDATE xxx SET memo1 = "adfsd" WHERE condition1 = 'satisfied'");
db.ExecuteNonQuery(cmd);
This query overwrites the previous values in the memo1.
I Cannot use MODIFY memo in C#.
How do I append a string to a already existing memo field in Foxpro using C# ?

Try making the command say:
UPDATE xxx SET memo1 = memo1 + "adfsd"

I think the issue is probably with GetSqlStringCommandWrapper which as far as I can see is deprecated.
This shouldn't be a problem to do, for example using the OLEDB provider:
var DBC = #"C:\mydata.dbc";
string ConnectionString = string.Format("Provider=VFPOLEDB.1;Data Source={0};Exclusive=false;Ansi=true;OLE DB Services = 0", DBC);
using (OleDbConnection testConnection = new OleDbConnection(ConnectionString))
{
OleDbCommand updateCommand = new OleDbCommand(#"update mytable set mymemo=alltrim(mymemo)+ttoc(datetime()) where thisfield='THISVALUE'", testConnection);
testConnection.Open();
updateCommand.ExecuteNonQuery();
Console.WriteLine(#"Finished - press ENTER.");
Console.ReadLine();
}

You need to parameterize your query.. Assuming your query wrapper gets the sql connection handle to the database. The VFP OleDB Provider uses "?" as a "place-holder" for parameters and must match the order as associated to your query.
I have a more detailed sample to a very similar question here...
Try something like
string whatToSetItTo = "this is a test string that can even include 'quotes'";
cmd = db.GetSqlStringCommandWrapper("UPDATE YourTable SET memo1 = ? WHERE someKeyColumn = ?");
cmd.Parameters.Add( "parmForMemoField", whatToSetItTo);
cmd.Parameters.Add( "parmForKeyColumn", "satisfied" );
db.ExecuteNonQuery(cmd);
Notice the parameters added in same sequence. whatever the string value is (or could even be integer, date, etc respective to your table structure, but your sample only was based on strings) the place-holders are filled in order. The values would update accordingly.

SQL Server CE WHERE statement behaving wrong? very confused

I am developing a windows mobile app. Right now I am just testing that it can correctly query the local SQL Server CE database. It works fine until I put a WHERE statement in.
Here is my code:
private void buttonStart_Click(object sender, EventArgs e)
{
System.Data.SqlServerCe.SqlCeConnection conn = new System.Data.SqlServerCe.SqlCeConnection(
("Data Source=" + (System.IO.Path.Combine(System.IO.Path.GetDirectoryName(System.Reflection.Assembly.GetExecutingAssembly().GetName().CodeBase), "ElectricReading.sdf") + ";Max Database Size=2047")));
try
{
// Connect to the local database
conn.Open();
System.Data.SqlServerCe.SqlCeCommand cmd = conn.CreateCommand();
SqlCeParameter param = new SqlCeParameter();
param.ParameterName = "#Barcode";
param.Value = "%" + textBarcode.Text.Trim() + "%";
// Insert a row
cmd.CommandText = "SELECT * FROM Main2 WHERE Reading LIKE #Barcode";
cmd.Parameters.Add(param);
cmd.ExecuteNonQuery();
DataTable data = new DataTable();
using (SqlCeDataReader reader = cmd.ExecuteReader())
{
if (reader.Read())
{
data.Load(reader);
}
}
if (data != null)
{
this.dataGrid1.DataSource = data;
}
}
finally
{
conn.Close();
}
The database contains this data:
Okay so you can see I changed the WHERE statement to use the Reading column just for testing purposes. When I enter "111" into the textbox and run --> it returns only the row where reading ="1111" and not the row that contains "111".
If I enter "1111" it does not return any data.
If I enter "1" it will return both the "1111" row and the "111" row which is the correct behavior.
However if I enter "11" it once again only returns the "1111" row.
Any other data entry of 2's or 9's attempting to return those rows does not work.
I'm not sure what is going on? This does not make any sense. It is not behaving like I would expect in any way shape or form. I know this must be a little confusing to read. I hope it makes enough sense to get some answers. Please help!
NOTE: I added the "%" before and after the text in an attempt to get better results. This is not desired.
EDIT <<<-----------------------I did have Reading = #Barcode, I just accidently typed Location for this question, that is not the problem.

Firstly, some things to note:
1) As other commentators have noted, use the Reading column, not the Location column. I know you have mentioned you are testing, but swapping around column names and then changing code isn't the easiest way to troubleshoot these things. Try to only change one thing at a time.
2) If Reading is numeric, you are going to have to convert the column value first.
So your query becomes:
"SELECT * FROM Main2 WHERE CONVERT(varchar, Reading) LIKE #Barcode";
Also see How to use parameter with LIKE in Sql Server Compact Edition for more help with working with parameters in SqlServerCE.
3) Set a parameter type on your SqlCEParameter. I've linked to the appropriate page in the code example below.
4) You are using ExecuteNonQuery for no reason. Just get rid of it in this context. It's for when you want to make a change to the database (like an insert, update, delete) or execute something (like a stored proc that can also insert, update, delete etc) that returns no rows. You've probably cut and paste this code from another place in your app :-)
5) Use using on disposable objects (see example below). This will make managing your connection lifecycle much simpler. It's also more readable (IMO) and will take care of issues when exceptions occur.
6) Use the using statement to import the BCL (Base Class Libraries) into your current namespace:
Add the following using statements to the top of your class (.cs). This will make using all of the .Net classes a lot simpler (and is much easier to read and less wear on your keyboard ;-)
using System.Data.SqlServerCe;
using System.IO;
using System.Reflection;
A more complete example would look like the following
private void buttonStart_Click(object sender, EventArgs e)
{
using(SqlCeConnection conn = new SqlCeConnection(
("Data Source=" + (Path.Combine(Path.GetDirectoryName(Assembly.GetExecutingAssembly().GetName().CodeBase), "ElectricReading.sdf") + ";Max Database Size=2047"))))
{
// Connect to the local database
conn.Open();
using(SqlCeCommand cmd = conn.CreateCommand())
{
SqlCeParameter param = new SqlCeParameter();
param.ParameterName = "#Barcode";
param.DBType = DBType.String; //Intellisense is your friend here but See http://msdn.microsoft.com/en-US/library/system.data.sqlserverce.sqlceparameter.dbtype(v=VS.80).aspx for supported types
param.Value = "%" + textBarcode.Text.Trim() + "%";
// SELECT rows
cmd.CommandText = "SELECT * FROM Main2 WHERE CONVERT(varchar, Reading) LIKE #Barcode";
cmd.Parameters.Add(param);
//cmd.ExecuteNonQuery(); //You don't need this line
DataTable data = new DataTable();
using (SqlCeDataReader reader = cmd.ExecuteReader())
{
data.Load(reader); //SqlCeDataReader does not support the HasRows property.
if(data.Rows.Count > 0)
{
this.dataGrid1.DataSource = data;
}
}
}
}
}
Intellisense should be able to clean up any errors with the above but feel free to ask for more help.
Finally, you also might be able to set the data source of the grid directly to a datareader, try it!
using (SqlCeDataReader reader = cmd.ExecuteReader())
{
dataGrid1.DataSource = reader;
}
You can then get rid of the DataTable.

Change the following line:
cmd.CommandText = "SELECT * FROM Main2 WHERE Location LIKE #Barcode";
to
cmd.CommandText = "SELECT * FROM Main2 WHERE Reading LIKE #Barcode";
You are comparing the wrong columns.