Write and read text to blob (mysql)

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C# WindowsForm
I have to memorize a simple text present in a TextBox
e.g: 
line1
line2
line3

into a BlobFiels MySql (medium Blob)
...

and then read and assign to TextBox

What I have tried:

byte[] byteBLOBData = (Byte[])(row["FIELDNAME"]);
String s = System.Text.Encoding.UTF8.GetString(byteBLOBData);

(Byte[])(row["FIELDNAME"])

row .... not recognized

what it is row ... object, variable ?

Posted 9-Dec-19 3:57am

Member 13174280

Updated 15-Dec-19 0:43am

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Richard MacCutchan 9-Dec-19 10:18am

What is row?

Ashutosh Gpta 9-Dec-19 10:43am

@Member 13174280, you have tried the solution then definlty you would have define the type of row, right, but anyways my impression seems to be you are using grid and row is type of DataRow and FIELDNAME is column name.

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OriginalGriff · Answer 1 · 2019-12-09T04:45:00

Solution 1

We can't tell: it needs the rest of that method to give context to the error message.
But ... at a guess, you are using a DataReader or a DataTable in a loop to access the data, and row should be related to that loop.

So look at the code around that line, and see what changes automatically each time round the loop - that is probably what you should be using instead of row

Posted 9-Dec-19 4:45am

OriginalGriff

Comments

Member 13174280 9-Dec-19 12:32pm

ok, thanks; my error on row
this is correct.

DataTable dtFoto = new DataTable();
dtFoto = gesdb.QryRead(conn, dtFoto, Query); //execute query

MemoryStream ms;

int x = 0;
foreach (DataRow row in dtFoto.Rows)
{
FileImg = row["description"].ToString();

byte[] byteBLOBData = (Byte[])(row["public_note"]);
textBox1.Text = Encoding.UTF8.GetString(byteBLOBData);
}

then Blob is
line1
line2
...
the result is line1/nline2/nline3/n
texBox1 does not apply the /n
and show line1line2line3

OriginalGriff 9-Dec-19 12:51pm

Well of course it won't!
If you did this:

int x = 1;
x = 2;
x = 3;
Console.WriteLine(x);

Would you expect it to write "3" or "6"?
You are doing the same thing with your TextBox - each time round the loop you set the value to the current string and discards all previous ones.

To assemble each on a separate line of a multiline Textbox, you need to either assemble all lines into an array of strings and set the Lines property, or add each line of text with a Environment.Newline separating them.

Member 13174280 9-Dec-19 13:44pm

this routine solve then \n

string newLine = Environment.NewLine;
int at = 0;
string app;
string app1 = "";

while (s.Length > 0)
{
at = s.IndexOf("\n");
app = s.Substring(0, at) + newLine;
s = s.Substring(at + 1);
app1 = app1 + app;
}

textBox1.Text = app1;

now show
line1
line2
...
linex

Patrice T 14-Dec-19 19:56pm

Use Improve question to update your question.
So that everyone can pay attention to this information.

Maciej Los · Answer 2 · 2019-12-15T00:44:00

Solution 4

I'd suggest to read MySQL documentation:
MySQL :: MySQL Connector/NET Developer Guide :: 4.10.2 Writing a File to the Database[^]
MySQL :: MySQL Connector/NET Developer Guide :: 4.10.3 Reading a BLOB from the Database to a File on Disk[^]

Posted 15-Dec-19 0:44am

Maciej Los