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Update query with certain parameters

Posted on 2013-02-06
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Last Modified: 2013-02-06
Hello,

I hope I can explain this without making myself sound an idiot.

I'm getting to grips with creating SQL adapters.  I can create an update command with parameters and pass those values in for the update with no problem.

The disadvantage of this as far as I can see is that you have to create a new update command every time you want to change a record to reflect the changes that you are making at that point.  My question is if it is possible to create a "global" update command for the table ( with all the columns in the table as parameters ) which will use the existing values for each column as the parameters values unless you provide new values for one or more of the parameters.

Does that make sense?
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Question by:Petermcg001
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5 Comments
 
LVL 42

Expert Comment

by:Meir Rivkin
ID: 38859433
you can do batch operations using datatable which means you modify your datatable instance and use the adapter to update your DB table:
Performing Batch Operations Using DataAdapters
you may use stored procedure if u need to update large number of rows.
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Author Comment

by:Petermcg001
ID: 38859588
Hello, thanks for looking at this.

It's not really what I was trying to get at.

Let's say I have a two column table called tblContacts with columns FirstName and LastName.

If I want to update just the first name my update command will be "UPDATE tblContacts SET FirstName  = @FirstNameParam WHERE....." and I then have to pass the first name value in.  If in a different form I want change the LastName I have to create another update command with "UPDATE tblContacts SET LastName = @LastNameParam WHERE....." and then provide the last name as a value for the parameter.

What I would like to achieve is to create one update command of "UPDATE tblContacts SET FirstName = @FirstNameParam, LastName = @LastNameParam WHERE....." which can be used anywhere in my application and where I can choose to provide a new value for any of the parameters but to take the existing value of a column for the parameter value for those columns which I don't want to change at that point.

Thanks
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LVL 42

Accepted Solution

by:
Meir Rivkin earned 2000 total points
ID: 38859786
create an update command builder which uses named parameters and can be invoke all the updates at once.

here full class:
   public class UpdateCommandBuilder
    {
        Dictionary<string, object> _updateParams = new Dictionary<string, object>();
        Dictionary<string, object> _whereParams = new Dictionary<string, object>();
        string _constring;
        string _table;

        public UpdateCommandBuilder(string connectionstring, string table)
        {
            _constring = connectionstring;
            _table = table;
        }

        public void AddWhere(string name, object value)
        {
            _whereParams.Add(name, value);
        }

        public void AddParam(string name, object value)
        {
            _updateParams.Add(name, value);
        }

        public int SubmitChanges()
        {
            string commandText = BuildCommandText();

            using (SqlConnection connection = new SqlConnection(_constring))
            {
                SqlCommand command = new SqlCommand(commandText.ToString(), connection);

                command.Parameters.AddRange(_whereParams.Select(n =>
                    new SqlParameter
                    {
                        ParameterName = "@" + n.Key,
                        Value = n.Value
                    }).ToArray());

                command.Parameters.AddRange(_updateParams.Select(n =>
                    new SqlParameter
                    {
                        ParameterName = "@" + n.Key,
                        Value = n.Value
                    }).ToArray());

                try
                {
                    connection.Open();
                    return command.ExecuteNonQuery();
                }
                catch (Exception ex)
                {
                    Console.WriteLine(ex.Message);

                }

                return 0;
            }
        }

        private string BuildCommandText()
        {
            var sb = new StringBuilder(string.Format("UPDATE {0} SET ", _table));
            foreach (var key in _updateParams.Keys)
            {
                sb.Append(string.Format("{0} = @{0},", key));
            }

            sb.Remove(sb.Length - 1, 1);

            if (_whereParams.Count > 0)
            {
                sb.Append(" WHERE ");
                foreach (var key in _whereParams.Keys)
                {
                    sb.Append(string.Format("{0} = @{0} AND ", key));
                }
            }

            sb.Remove(sb.Length - 3, 3);
            return sb.ToString();
        }
    }

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example usage:
UpdateCommandBuilder cmdbuilder = new UpdateCommandBuilder("your-connection-string", "yout-table");
            cmdbuilder.AddParam("FirstName", "Joe");
            cmdbuilder.AddParam("LastName", "Brown");
            cmdbuilder.AddParam("Age", 37);
            cmdbuilder.AddWhere("ID", 1);
            cmdbuilder.AddWhere("IsActive", true);
            cmdbuilder.SubmitChanges();

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the result sql will be:
UPDATE Employee SET FirstName = @FirstName,LastName = @LastName,Age = @Age WHERE ID = @ID AND IsActive = @IsActive 

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LVL 25

Expert Comment

by:jogos
ID: 38859905
When you use "SET FirstName = @FirstNameParam, LastName = @LastNameParam" then you have to provide both @FirstNameParam and @LastNameParam.  
If you want to reuse that code then you must provide also the value of the column that is not changed.  This means that you only can do this if you know that value in your programm.  
There can be ugly workarounds for 'NOT NULL'-fields providing a DbNULL-value and then using the isnull in your update. If you pass the null-value then it is set to itself.

.... but again ugly
UPDATE tblContacts SET FirstName  = isnull(@FirstNameParam,FirstName)
,LastName = isnull(@LastNameParam, LastName)
 

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Author Closing Comment

by:Petermcg001
ID: 38860069
Thanks!
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