This question already has answers here:
Check for column name in a SqlDataReader object
(27 answers)
Closed 8 years ago.
Is there a way to see if a field exists in an IDataReader-based object w/o just checking for an IndexOutOfRangeException?
In essence, I have a method that takes an IDataReader-based object and creates a strongly-typed list of the records. In 1 instance, one data reader has a field that others do not. I don't really want to rewrite all of the queries that feed this method to include some form of this field if I don't have to. The only way I have been able to figure out how to do it so far is to throw the 1 unique field into a try/catch block as shown below.
try
{
tmp.OptionalField = reader["optionalfield"].ToString();
}
catch (IndexOutOfRangeException ex)
{
//do nothing
}
Is there a cleaner way short of adding the "optional field" to the other queries or copying the loading method so 1 version uses the optional field and the other doesn't?
I'm in the 2.0 framework also.
I ended up finding a solution using the reader.GetName(int) method. I created the below method to encompass the logic.
public bool ColumnExists(IDataReader reader, string columnName)
{
for (int i = 0; i < reader.FieldCount; i++)
{
if (reader.GetName(i).Equals(columnName, StringComparison.InvariantCultureIgnoreCase))
{
return true;
}
}
return false;
}
The following will give you a list of the column name strings given a data reader.
(Remember the results are based on the last read so it may not be the same depending on what the reader read).
var cols = reader.GetSchemaTable()
.Rows
.OfType<DataRow>()
.Select(row => row["ColumnName"]);
Or to check if a column exists:
public bool ColumnExists(IDataReader reader, string columnName)
{
return reader.GetSchemaTable()
.Rows
.OfType<DataRow>()
.Any(row => row["ColumnName"].ToString() == columnName);
}
Enumerable.Range(0, reader.FieldCount).Any(i => reader.GetName(i) == "ColumnName")
This should work, try this:
private static bool ColumnExists(SqlDataReader reader, string columnName)
{
using (var schemaTable = reader.GetSchemaTable())
{
if (schemaTable != null)
schemaTable.DefaultView.RowFilter = String.Format("ColumnName= '{0}'", columnName);
return schemaTable != null && (schemaTable.DefaultView.Count > 0);
}
}
Appears I stand corrected. I know your actual column names are in there, but I was going down the wrong path. This reference helped clear things up a bit, but I'm still not sure if there's an elegant way of doing it. Adapted from the above link, you could get a list of all of your columns with the following:
List<string> myCols = new List<string>();
DataTable schema = reader.GetSchemaTable();
foreach (DataRow row in schema.Rows)
{
myCols.Add(row[schema.Columns["ColumnName"]]);
}
Unfortunately it appears you can only access schema.Rows by index, so I'm not sure you can get around looping through the rows first before checking by name. In that case, your original solution seems far more elegant!
Note: my original answer suggested checking for presence of a column simply by: reader.GetSchemaTable().Columns["optionalfield"].
Load it into a DataTable and then you can check for column:
DataTable dataTable = new DataTable();
dataTable.Load(reader);
foreach (var item in dataTable.Rows)
{
bool columnExists = item.Table.Columns.Contains("ColumnName");
}
Don't need so much complication, just this:
bool bFieldExists = datareader.GetSchemaTable().Columns.Contains(strFieldName);
Related
UPDATE
I think I have found what is causing the issue here https://stackoverflow.com/a/5665600/19393524
I believe my issue lies with my use of .DefaultView. The post thinks when you do a sort on it it is technically a write operation to the DataTable object and might not propagate changes made properly or entirely. It is an interesting read and seems to answer my question of why passing valid data to a DataRow is throwing this exception AFTER I make changes to the datatable
UPDATE:
Let me be crystal clear. I have already solved my problem. I would just like to know why it is throwing an error. In my view the code should work and it does.. the first run through.
AFTER I have already deleted the column then added it back (run this code once)
When I debug my code line by line in Visiual studio and stop at the line:
data.Rows[i].SetField(sortColumnNames[k], value);
the row exists
the column exisits
value is not null
sortColumnNames[k] is not null and contains the correct column name
i is 0
Yet it still throws an exception. I would like to know why. What am I missing?
Sorry for the long explanation but this one needs some context unfortunately.
So my problem is this, I have code that sorts data in a DataTable object by column. The user picks the column they want to sort by and then my code sorts it.
I ran into an issue where I needed numbers to sort as numbers not strings (all data in the table is strings). eg (string sorting would result in 1000 coming before 500)
So my solution was to create a temporary column that uses the correct datatype so that numbers get sorted properly and the original string data of the number remains unchanged but is now sorted properly. This worked perfectly. I could sort string numeric data as numeric data without changing the formatting of the number or data type.
I delete the column I used to sort afterwards because I use defaultview to sort and copy data to another DataTable object.
That part all works fine the first time.
The issue is when the user needs to do a different sort on the same column. My code adds back the column. (same name) then tries to add values to the column but then I get a null reference exception "Object not set to an instance of an object"
Here is what I've tried:
I've tried using AcceptChanges() after deleting a column but this did nothing.
I've tried using column index, name, and column object returned by DataTable.Columns.Add() in the first parameter of SetField() in case it was somehow referencing the "old" column object I deleted (this is what I think the problem is more than likely)
I've tried changing the value of the .ItemArray[] directly but this does not work even the first time
Here is the code:
This is the how the column names are passed:
private void SortByColumn()
{
if (cbAscDesc.SelectedIndex != -1)//if the user has selected ASC or DESC order
{
//clears the datatable object that stores the sorted defaultview
sortedData.Clear();
//grabs column names the user has selected to sort by and copies them to a string[]
string[] lbItems = new string[lbColumnsToSortBy.Items.Count];
lbColumnsToSortBy.Items.CopyTo(lbItems, 0);
//adds temp columns to data to sort numerical strings properly
string[] itemsToSort = AddSortColumns(lbItems);
//creates parameters for defaultview sort
string columnsToSortBy = String.Join(",", itemsToSort);
string sortDirection = cbAscDesc.SelectedItem.ToString();
data.DefaultView.Sort = columnsToSortBy + " " + sortDirection;
//copies the defaultview to the sorted table object
sortedData = data.DefaultView.ToTable();
RemoveSortColumns(itemsToSort);//removes temp sorting columns
}
}
This is where the temp columns are added:
private string[] AddSortColumns(string[] items)//adds columns to data that will be used to sort
//(ensures numbers are sorted as numbers and strings are sorted as strings)
{
string[] sortColumnNames = new string[items.Length];
for (int k = 0; k < items.Length; k++)
{
int indexOfOrginialColumn = Array.IndexOf(columns, items[k]);
Type datatype = CheckDataType(indexOfOrginialColumn);
if (datatype == typeof(double))
{
sortColumnNames[k] = items[k] + "Sort";
data.Columns.Add(sortColumnNames[k], typeof(double));
for (int i = 0; i < data.Rows.Count; i++)
{
//these three lines add the values in the original column to the column used to sort formated to the proper datatype
NumberStyles styles = NumberStyles.Any;
double value = double.Parse(data.Rows[i].Field<string>(indexOfOrginialColumn), styles);
bool test = data.Columns.Contains("QtySort");
data.Rows[i].SetField(sortColumnNames[k], value);//this is line that throws a null ref exception
}
}
else
{
sortColumnNames[k] = items[k];
}
}
return sortColumnNames;
}
This is the code that deletes the columns afterward:
private void RemoveSortColumns(string[] columnsToRemove)
{
for (int i = 0; i < columnsToRemove.Length; i++)
{
if (columnsToRemove[i].Contains("Sort"))
{
sortedData.Columns.Remove(columnsToRemove[i]);
}
}
}
NOTE:
I've been able to fix the problem by just keeping the column in data and just deleting the column from sortedData as I use .Clear() on the sorted table which seems to ensure the exception is not thrown.
I would still like an answer though as to why this is throwing an exception. If I use .Contains() on the line right before the one where the exception is thrown is says the column exists and returns true and in case anyone is wondering the params sortColumnNames[k] and value are never null either.
Your problem is probably here:
private void RemoveSortColumns()
{
for (int i = 0; i < data.Columns.Count; i++)
{
if (data.Columns[i].ColumnName.Contains("Sort"))
{
data.Columns.RemoveAt(i);
sortedData.Columns.RemoveAt(i);
}
}
}
If you have 2 columns, and the first one matches the if, you will never look at the second.
This is because it will run:
i = 0
is i < columns.Count which is 2 => yes
is col[0].Contains("sort") true => yes
remove col[0]
i = 1
is i < columns.Count which is 1 => no
The solution is to readjust i after the removal
private void RemoveSortColumns()
{
for (int i = 0; i < data.Columns.Count; i++)
{
if (data.Columns[i].ColumnName.Contains("Sort"))
{
data.Columns.RemoveAt(i);
sortedData.Columns.RemoveAt(i);
i--;//removed 1 element, go back 1
}
}
}
I fixed my original issue by changing a few lines of code in my SortByColumn() method:
private void SortByColumn()
{
if (cbAscDesc.SelectedIndex != -1)//if the user has selected ASC or DESC order
{
//clears the datatable object that stores the sorted defaultview
sortedData.Clear();
//grabs column names the user has selected to sort by and copies them to a string[]
string[] lbItems = new string[lbColumnsToSortBy.Items.Count];
lbColumnsToSortBy.Items.CopyTo(lbItems, 0);
//adds temp columns to data to sort numerical strings properly
string[] itemsToSort = AddSortColumns(lbItems);
//creates parameters for defaultview sort
string columnsToSortBy = String.Join(",", itemsToSort);
string sortDirection = cbAscDesc.SelectedItem.ToString();
DataView userSelectedSort = data.AsDataView();
userSelectedSort.Sort = columnsToSortBy + " " + sortDirection;
//copies the defaultview to the sorted table object
sortedData = userSelectedSort.ToTable();
RemoveSortColumns(itemsToSort);//removes temp sorting columns
}
}
Instead of sorting on data.DefaultView I create a new DataView object and pass data.AsDataView() as it's value then sort on that. Completely gets rid of the issue in my original code. For anyone wondering I still believe it is bug with .DefaultView in the .NET framework that Microsoft will probably never fix. I hope this will help someone with a similar issue in the future.
Here is the link again to where I figured out a solution to my problem.
https://stackoverflow.com/a/5665600
This question already has answers here:
Remove Single Quotes From All Cells in a DataTable - Creating New Table - Using LINQ in Vb.Net
(2 answers)
Closed 3 years ago.
How to replace double quotes of all rows of DataTable using Linq in C#?
I tried below but I need more optimized code for same purpose
int columnIndex = 0;
dtExcelData.Rows.RemoveAt(0);
foreach (DataColumn excelSheetColumns in dtExcelData.Columns)
{
int rowIndex = 0;
foreach (DataRow row in dtExcelData.Rows)
{
dtExcelData.Rows[rowIndex][columnIndex] = dtExcelData.Rows[rowIndex][columnIndex].ToString().Replace("\"", "");
rowIndex++;
}
columnIndex++;
}
Please suggest
You could make use of DataRow.ItemArray. For example
foreach(var row in dtExcelData.Rows.Cast<DataRow>())
{
row.ItemArray = row.ItemArray.Select(x=>x.ToString().Replace("\"","")).ToArray();
}
You should
be aware you remove the first row, if you write results back to your data store you will lose this row.
ask yourself why you iterare over Columns and rows if you never use the objects. Why don't you simply use a for loop over rowIndex and columnIndex.
think about only processing data fields that really are a string.ToString() turns everything into a string, then you overwrite any kind of data field type with a string. Better test for "is String" and then cast the field into (String).
think about getting every row, then process every column in this row. This could be faster to execute, but even if it isn't then still is more understandable (at least to me).
I have added code here because code is better other than URL, You can try this below code:
That is already mentioned in below URL
Remove Single Quotes From All Cells in a DataTable - Creating New Table - Using LINQ in Vb.Net
dtExcelData.Rows.RemoveAt(0);
DataTable clone = dtExcelData.Clone();
string t;
var qry = from DataRow row in dtExcelData.Rows
let arr = row.ItemArray
select Array.ConvertAll(arr, s =>
(t = s as string) != null
&& t.StartsWith("\"")
&& t.EndsWith("\"") ? t.Trim('\"') : s);
foreach (object[] arr in qry)
{
clone.Rows.Add(arr);
}
what I'm trying to do: I have a large datatable, and I'm going through a list of strings where some of them are in the datatable and some aren't. I need to make a list of those that are, and count those that aren't.
This is my code part:
DataRow[] foundRows;
foundRows = DTgesamt.Select("SAP_NR like '%"+SAP+"%'");
if (AreAllCellsEmpty(foundRows[0]) == false && !(foundRows[0]==null))
{
list.Add(SAP);
}
else
{
notfound++;
}
public static bool AreAllCellsEmpty(DataRow row)
{
if (row == null) throw new ArgumentNullException("row");
for (int i = row.Table.Columns.Count - 1; i >= 0; i--)
{
if (!row.IsNull(i))
{
return false;
}
}
return true;
}
DTgesamt ist a large DataTable. "SAP" is a string that is in the first column of the DataTable, but not all of them are included. I want to count the unfound ones with the int "notfound".
The problem is, the Select returns an empty DataRow {System.Data.DataRow[0]} when it finds nothing.
I'm getting the errormessage Index out of array area.
The two statements in the if-clause are what I read on the internet but they don't work. With only the 2nd statement it just adds all numbers to the list, with the first it still gives this error.
Thanks for any help :)
check count of items in foundRows array to avoid IndexOutOfRange exception
foundRows = DTgesamt.Select("SAP_NR like '%"+SAP+"%'");
if (foundRows.Length > 0 && AreAllCellsEmpty(foundRows[0])==false)
list.Add(SAP);
else
notfound++;
The found cells cannot be empty. Your select statement would be wrong. So what you actually need is:
if (DTgesamt.Select("SAP_NR like '%"+SAP+"%'").Any())
{
list.Add(SAP);
}
else
{
notfound++;
}
You probably don't even need the counter, when you can calculate the missed records based on how many SAP numbers you had and how many results you got in list.
If you have an original list or array of SAP numbers, you could shorten your whole loop to:
var numbersInTable = originalNumbers.Where(sap => DTgesamt.Select("SAP_NR like '%"+sap+"%'").Any()).ToList();
var notFound = originalNumbers.Count - numbersInTable.Count;
I have an application which stores a user selected value to the value in my dataset filled datatable. I need to set another column in the table based on this comparison. But the comparison is not working. It always returns false, not entering in the if condition.
foreach (DataRow dr in dsQuestions.Tables[0].Rows)
{
if (dr["Data"] == indicater[0])
{
dr["IsSelected"] = true;
}
}
indiactor[0] is a string array and dr["data"] is also of type string but it shows a warning that it needs to a string type.
The DataRow indexer returns the field at that index as object not as string.
I would recommend to use the strongly typed Field-extension method which also supports nullables:
if (dr.Field<String>("Data") == indicater[0]){}
... and the SetField method that also support nullable types:
dr.SetField("IsSelected", true);
Update if indicater[0] is really a string[] (not a single string), how do you want to compare a string with a string[]? If you for example want to check if the array contains this data:
if (indicater[0].Contains(dr.Field<String>("Data"))){}
That would also explain why it never enters the if: because == only compares strings by equality, other types which don't have overridden the ==-operator will compare only the reference. A string is never the same reference as a string[]. But you don't get a compile time error because you can compare an object with everything else.
First of all string can't compare using == you should use equals method:
foreach (DataRow dr in dsQuestions.Tables[0].Rows)
{
if (dr["Data"].tostring().Equals(indicater[0]))
{
dr["IsSelected"] = true;
}
May be useful for you
DataRow[] result = table.Select("Id = 1");
foreach (DataRow row in result)
{
if (row[0].Equals(indicater[0]))
{
//IsSelected
row[1]=true;
Console.WriteLine("{0}", row[0]);
}
}
Try this:
foreach (DataRow dr in dsQuestions.Tables[0].Rows)
{
if (dr["Data"].ToString() == indicater[0].ToString())
{
Convert.ToBoolean(dr["IsSelected"].ToString()) = true;
}
}
I'm trying to figure out if my data table contains a certain row. So I used the .Contains method, but when I tried to run my program I was met with a MissingPrimaryKeyException which I can't figure out.
DataTable table = dataQuery.executeQuery();
foreach(DataRow row in table.Rows)
{
if(table.Rows.Contains("certainRow"))
{
blah blah blah
...
I am only getting the exception the 2nd time I call table.Rows which is what is making no sense to me. If my table didn't have a primary key, wouldn't it have given me an error in the foreach call?
EDIT: I just realized that Contains did something else than I thought it did. Matthijs... yes that is kind of what I want. I need to know if "certainRow" is actually a row that exists otherwise I cannot manipulate the data in that row.
Unfortunately I am new to C# and haven't programmed in anything in over 5years so I cannot figure out if there is a method that does what I want. Or if I need to create something myself.
EDIT#2:
I figured out a solution to my problem using the DataTableReader.
private bool doesExist(string rowName, DataTable table)
{
bool value = false;
DataTableReader reader = new DataTableReader(table);
while (reader.Read())
{
for (int i = 0; i < reader.FieldCount; i++)
{
if (reader.GetValue(i) == rowName)
{
value = true;
}
}
}
return value;
}
You should be able to use the DataTableReader, more information can be found here.
An example, would be:
private static DataTable GetCustomer()
{
DataTable table = new DataTable();
DataColumn id = table.Columns.Add(#"Id", typeof(int));
table.Columns.Add(#"Name", typeof(string));
table.PrimaryKey = new DataColumn[] { id };
table.Rows.Add(new object[] { 1, #"John" });
return table;
}
The above code will build a table, as you see you define your Primary Key and add the Content. That is how you would build the table. Now to read, you would:
using(DataTableReader reader = new DataTableReader(new DataTable[] { customer }))
{
do
{
if(reader.HasRows)
{
// Do Something
}
} while (reader.NextResult());
}
As you can see it validates the row exist, then performs a task. Very simple example, hope it helps.
The .Contains will return a boolean for a true or false value.
In regards to your comment, you can call reader[#"ColumnName"] and it should attempt to read it without an issue. So if:
if(reader[#"ColumnName"] != DBNull.Value)
{
// Do Something.
}
You could just write:
bool contains = table.Rows.Cast<DataRow>().SelectMany(r => r.ItemArray).Contains(value);