Re: Remoting problems with ArrayList return - C# Discussion Boards

21-Sep-06 13:17

Greetings!

I'm trying to connect to a database and read certain fields from it. I'm unable to read any fields from it and would appreciate your help debugging/fixing the problem.

Here is what I have:

1. A file that acts has the database interface code:

<br />
 public class AppDatabaseInterface<br />
    {<br />
<br />
        // Directory names<br />
        private string m_cstrDefaultdbDir = "C:\\";<br />
<br />
        // File names<br />
        private const string m_cstrDBFileName = "DefaultDatabase.mdb";<br />
<br />
        private System.Data.OleDb.OleDbConnection m_dbConn;<br />
<br />
        public AppDatabaseInterface()<br />
        {<br />
            // Determine the App Root directory when this object is constructed<br />
            System.Reflection.Assembly assm =<br />
                System.Reflection.Assembly.GetAssembly(System.Type.GetType("AppDatabase.AppDatabaseInterface"));<br />
            m_cstrDefaultdbDir = System.IO.Path.GetDirectoryName(assm.CodeBase.ToString());<br />
            m_cstrDefaultdbDir = m_cstrDefaultdbDir.Remove(0, 6);	// Removes the leading file:\ header from the path.<br />
<br />
            OpenDatabase();<br />
        }<br />
<br />
<br />
        private void OpenDatabase()<br />
        {<br />
            lock (this)<br />
            {<br />
                // If the database connection hasn't been initialized, create it.  <br />
                // If it exists and is currently connected, close the connection<br />
                // as we are about to establish a new connection.<br />
                if (m_dbConn == null)<br />
                {<br />
                    m_dbConn = new OleDbConnection();<br />
                }<br />
                else<br />
                {<br />
                    if (m_dbConn.State != ConnectionState.Closed)<br />
                    {<br />
                        m_dbConn.Close();<br />
                    }<br />
                }<br />
<br />
                // Create the new connection string and try and attach to the new database.<br />
                try<br />
                {<br />
                    m_dbConn.ConnectionString = string.Format(<br />
                         @"Provider=Microsoft.Jet.OLEDB.4.0; Data Source={0}\{1};",<br />
                         m_cstrDefaultdbDir, m_cstrDBFileName);<br />
                }<br />
                catch<br />
                {<br />
                    Console.WriteLine("Could not open database");<br />
                }<br />
                m_dbConn.Open();<br />
<br />
            }<br />
        }<br />

2. The actual UI form

<br />
public partial class frmAppDatabase: Form<br />
    {<br />
        AppDatabaseInterface m_database;<br />
<br />
        public frmSpeakerDatabase()<br />
        {<br />
            InitializeComponent();<br />
<br />
            m_database = new AppDatabaseInterface();<br />
<br />
            string[] strSpeakerMakes = m_database.Makes;<br />
<br />
            for (int i = 0; i < strSpeakerMakes.Length; i++)<br />
            {<br />
                cbSpeakerMakes.Items.Add(strSpeakerMakes[i]);<br />
            }<br />
      }<br />

What I want this portion of the code to do is to fill in the combobox with the various items from the specified field in the database. However, I see nothing.

The Access file is in the \bin\debug directory of the project.

Could you please advice me as to what is wrong?

Thanks!

Guffa21-Sep-06 20:53

21-Sep-06 20:53

TheBlindWatchmaker wrote:
However, I see nothing.

You see nothing? Not even the error message?

You are trying to use the property "Makes", but you have not created any property with that name. What do you expect to happen?

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TheBlindWatchmaker22-Sep-06 5:15

22-Sep-06 5:15

Oops! My mistake!

Here's the "Makes" method in the AppDatabaseInterface.cs file

<br />
        public string[] Models(string make)<br />
        {<br />
            {<br />
                OleDbDataReader dbr = null;<br />
                ArrayList Models = new ArrayList();<br />
<br />
                OleDbCommand cmd = new OleDbCommand(string.Format("SELECT * FROM {0};", "Speakers"), m_dbConn);<br />
                //OleDbCommand cmd = new OleDbCommand(string.Format("SELECT * FROM {0} WHERE {1} = {2};", "Speakers", "MAKE", make), m_dbConn);<br />
                dbr = cmd.ExecuteReader();<br />
<br />
                // Read each record one at a time ...<br />
                while (dbr.Read())<br />
                {<br />
                    // Load our arrays with the Field names<br />
                    // and values.<br />
<br />
                    string dbMake = "";<br />
                    string model= "";<br />
                    for (int it = 0; it < dbr.FieldCount; it++)<br />
                    {<br />
                        string strField = dbr.GetName(it);<br />
                        if (strField == "MAKE")<br />
                        {<br />
                            dbMake = (string)dbr.GetValue(it);<br />
                        }<br />
                        if (strField == "MODEL")<br />
                        {<br />
                            model = (string)dbr.GetValue(it);<br />
                        }<br />
                    }<br />
                    if (dbMake == make)<br />
                        Models.Add(model);<br />
<br />
                }<br />
                string[] strModels = new string[Models.Count];<br />
                int i = 0;<br />
                foreach (object o in Models)<br />
                {<br />
                    strModels[i++] = (string)o;<br />
                }<br />
                return strModels;<br />
            }<br />
        }<br />

Thanks!

Guffa22-Sep-06 7:29

22-Sep-06 7:29

TheBlindWatchmaker wrote:
Here's the "Makes" method in the AppDatabaseInterface.cs file

No, it isn't.

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TheBlindWatchmaker22-Sep-06 7:53

22-Sep-06 7:53

Damnit! I'm really inept today! Apologies, apologies!

This might be it! Smile | :)

<br />
 public string[] Makes<br />
        {<br />
            get<br />
            {<br />
                OleDbDataReader dbr = null;<br />
                ArrayList Makes = new ArrayList();<br />
<br />
                OleDbCommand cmd = new OleDbCommand(string.Format("SELECT * FROM {0};", "Speakers"), m_dbConn);<br />
                dbr = cmd.ExecuteReader();<br />
<br />
                // Read each record one at a time ...<br />
                while (dbr.Read())<br />
                {<br />
                    // Load our arrays with the Field names<br />
                    // and values.  NOTE: Reloading the field<br />
                    // names over and over again is probably<br />
                    // redundant, but I'm not sure that the order<br />
                    // column names are returned is fixed.<br />
                    for (int it = 0; it < dbr.FieldCount; it++)<br />
                    {<br />
                        string strField = dbr.GetName(it);<br />
                        if (strField == "MAKE")<br />
                        {<br />
                            string make = (string)dbr.GetValue(it);<br />
                            bool found = false;<br />
                            foreach (object o in Makes)<br />
                            {<br />
                                if ((string)o == make)<br />
                                {<br />
                                    found = true;<br />
                                    break;<br />
                                }<br />
                            }<br />
                            if (found)<br />
                                Makes.Add(make);<br />
                            break;<br />
                        }<br />
<br />
                    }<br />
<br />
                }<br />
                string[] strMakes = new string[Makes.Count];<br />
                int i= 0;<br />
                foreach (object o in Makes)<br />
                {<br />
                    strMakes[i++] = (string)o;<br />
                }<br />
                return strMakes;<br />
            }<br />
        }<br />

Guffa22-Sep-06 9:39

22-Sep-06 9:39

I see. The method does exactly what it should, and returns an empty array.

You only add to the ArrayList duplicates of values that already exist in the list, but as you start with an empty list, there are never any duplicates, so it will always remain empty.

I guess that your intention was to add the values that aren't duplicates?

In that case, why don't you just get the unique values from the database in the first place? And if you specify what field you want instead of using "select *", you don't have to loop through the fields looking for the one you want.

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TheBlindWatchmaker22-Sep-06 9:53

22-Sep-06 9:53

Hi Guffa,

The Makes field has, say, 10 speakers from Mfr1, 10 from Mfr2 etc. I want the combo box to show Mfr1, Mfr2 and so on.

How would you suggest I do this?

Thanks for your time!

Guffa22-Sep-06 10:37

PathTooLongException, Work around? [modified]

22-Sep-06 10:37

Select only the field containing the data that you want, and use the distinct keyword to get only one of each value.

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James_12321-Sep-06 12:34

James_123

21-Sep-06 12:34

Hi,

I'm trying to write as a small project a custom file explorer in C# however I've hit a rather annoying problem... When a file is > 260 characters long (yeah, I know people shouldn't have files that long, but they do) it'll throw the PathTooLongException fine, but what do you do next?

I was hoping I'd be able to catch that exception and at the same time still get the file size and other information I need to display but no such luck.

Is there any work-around's to fix this, or would the only acceptable solution be to write a custom library that properly wraps the Win32 API functions which are able to get the sizes/other information of > 260 char files? If so does anyone know an open-source library already made to do this, or will I need to make one?

Thanks! Smile | :)

VS2005: Unsafe mode in web service?

Goalie3521-Sep-06 11:24

Goalie35

21-Sep-06 11:24

I'm able to set unsafe mode in a console application by checking the checkbox in "Project Properties -> Build -> Allow unsafe code" however that option isn't available in a web service project.

So how can I set a web service project to unsafe mode?

Thanks.

-Goalie35

String with escaped squences...

e-laj21-Sep-06 11:22

e-laj

21-Sep-06 11:22

Is there a simple way to parse a string that contains escape character to the appropriate string, and vise versa?
For example, given the following string:
"hello\tthere"
should be parsed to:
"hello there"
and vs.
I need these methods because i let the user to enter escape chracters within the strings.

Thnaks!

Alaric_21-Sep-06 11:41

Alaric_

21-Sep-06 11:41

*simple* solution....as you asked. If you know every one of your escape characters (say you only use 2 for illustrative purposes... '/t' and '/n') you can add each one of them to a string array. Then whenever you need to parse your input string, call inputString.Split(delimiterList) where delimiterList is your array of characters. That parses your text as you requested, but I don't think you really want what you asked. ...If you allow users to insert escape characters, why would you want to eliminate them whenever you parse the input string? I think what you are actually asking is for an algorithm to perform character substitution for a particular escape sequence. Am I right?

Christian Graus21-Sep-06 11:45

Christian Graus

21-Sep-06 11:45

Escape characters are in your text when you enter the constant, but in the string itself, they become ( for example ) tabs and so on.

If you have a string which actually contains the \t, etc, then you need to use string.Replace to remove them, if that's what you need.

Christian Graus - Microsoft MVP - C++
Metal Musings - Rex and my new metal blog

Alaric_21-Sep-06 11:49

Alaric_

21-Sep-06 11:49

Please give a more illustrative example of what you are trying to accomplish. Are you saying that '\t' is supposed to represent a single whitespace character? In the original reply that I made, I assumed that 'hello' and 'there' were 2 seperate tokens created from parsing a string with a given delimiter. I think you really meant that you want to traverse the string and perform a character substitution based upon your defined escape sequences.