Develop Reference

How do I quickly convert DataTable to IList<myType>

In my sample, i tried to view the pivotal information in Grid control with given items source. In this case to pass the items source, i need to convert the DataTable into IList<myType> in C#.
I have tried all the traditional conversion methods including the below code to convert the DataTable into IList.
dt.AsEnumerable().Cast<object>().ToList()
But the all the traditional methods are not helpful for me since, i don't know exactly what are the objects are used and their types in respective columns in DataTable. Also the DataTable having more number of columns and rows.
For example, I am having the below column values in my data table.
PlanRowPID,PlanRowClass,PlanRowVendor,PlanRowColor
PID 0,CLASS 8,VENDOR A,COLOR D
PID 1,CLASS 7,VENDOR B,COLOR C
PID 2,CLASS 9,VENDOR C,COLOR B
PID 3,CLASS 6,VENDOR D,COLOR B
And finally i want to do the following pro-grammatically,
IList<myType> list = new IList<myType>;
list.Add(new myType() {PlanRowPID = "PID 0",PlanRowClass = "CLASS 8",PlanRowVendor = "VENDOR A",PlanRowColor=COLOR D});
list.Add(new myType() {PlanRowPID = "PID 1",PlanRowClass = "CLASS 7",PlanRowVendor = "VENDOR B",PlanRowColor=COLOR C});
list.Add(new myType() {PlanRowPID = "PID 2",PlanRowClass = "CLASS 9",PlanRowVendor = "VENDOR C",PlanRowColor=COLOR B});
In my application I have more than 10000 data columns, so it is not possible to add each and every object from data table into list.I need to spend more time and knowledge to find the data type of each columns available in DataTable and then create the properties based on their types for myType class.
So please provide any optimal and quickest way to convert the DataTable into IList<myType>.

In this case to pass the items source, i need to convert the DataTable into IList in C#.
Can't you just set the ItemsSource property to the DefaultView of the DataTable?
dataGrid.ItemsSource = dt.DefaultView;
Then there is no need to convert it to a list.
DataView implements IList.

Please try,
private static List<T> ConvertDataTable<T>(DataTable dt)
{
List<T> data = new List<T>();
foreach (DataRow row in dt.Rows)
{
T item = GetItem<T>(row);
data.Add(item);
}
return data;
}
private static T GetItem<T>(DataRow dr)
{
Type temp = typeof(T);
T obj = Activator.CreateInstance<T>();
foreach (DataColumn column in dr.Table.Columns)
{
foreach (PropertyInfo pro in temp.GetProperties())
{
if (pro.Name == column.ColumnName)
pro.SetValue(obj, dr[column.ColumnName], null);
else
continue;
}
}
return obj;
}
Example to invoke,
List<Student> studentDetails = new List<Student>();
studentDetails = ConvertDataTable<Student>(dt);
Source :- http://www.c-sharpcorner.com/UploadFile/ee01e6/different-way-to-convert-datatable-to-list/

Get name of variable without calling it

I have DataTable object with test data:
DataTable testData = new DataTable();
I'd like to assign data to variables which are the same as column names. I can do it like this:
string foo = testData.Rows[1]["foo"].ToString();
string bar = testData.Rows[1]["bar"].ToString();
or:
string foo = testData.Rows[1][nameof(foo)].ToString();
string bar = testData.Rows[1][nameof(bar)].ToString();
But, I dont want to call variable name every time, I'd like to use somethink like this:
string foo = testData.Rows[1][nameof(this)].ToString();
string bar = testData.Rows[1][nameof(this)].ToString();
Is it possible?

Why do you considder
string foo = testData.Rows[1][nameof(foo)].ToString();
to me more elegant than
string anyName = testData.Rows[1]["foo"].ToString();
You´d have to provide the name anyway. However variable-names don´t mean anything and are just arbitrary to be more readable.
Instead of relying on variable-names why not create a list of names and access the rows by the elements wthin that list?
var myList = new List<string> {"foo", "bar", ... };
Now you can just loop your list and get the rows value:
foreach(var name in myList)
{
var a = testData.Rows[1][name].ToString();
// do something with a
}

You probably want a class to represent the data in the row. You could then populate an object with those properties, either using reflection or serialization. Here's a possibility using simple reflection:
class MyRow
{
public string foo { get; set; }
public string bar { get; set; }
}
var row = testData.Rows[1];
var myRow = new MyRow();
foreach (DataColumn col in testData.Columns)
{
var prop = typeof(MyRow).GetProperty(col.ColumnName);
prop.SetValue(myRow, (string)(row[col] ?? string.Empty), null);
}
You now have an object that has properties of foo and bar.
Or, using serialization instead, it looks like the DataTable serializes nicely into a collection of objects so you can serialize the whole table, then grab the record you want after you deserialize the table:
var tableJson = JsonConvert.SerializeObject(testData);
myRow = JsonConvert.DeserializeObject<MyRow[]>(tableJson)[1];

loop through columns:
foreach(DataColumn col in testData.Columns)
{
var colValue = testData.Rows[1][col.ColumnName];
}

DataGridView with covariance?

I have code like below (I've generified and reduced it to represent just the issue at hand). The code works, that is it takes in a DataGridView.DataSource and ulitmately, using EPPlus, outputs the data to an Excel file. My question relates to covariance and how to use it, I think.
So you see it builds newList based on the type that it has found in the DataSource. Then a little further down it adds the data using the Properties, someClassObject.Name, .Address and .Phone that are unique to this type.
My problem is that there are about 75 different classes that could be passed in through the DataGridView parameter. Each class has its own unique properties (i.e. not necessarily Name, Address, Phone) though all of the objects in given DataGridView.DataSource are of the same class.
I could have a giant switch statement based on type.FullName and then each would have its own for loop to assign the Property values to the cell. That would work but would be incredibly cumbersome. Is there a better way to do this?
public void openExcelReport(ref DataGridView dataGridView, bool bolSave = false, bool bolOpen = true, string pageTitle = "EXPORTED DATA")
{
// put dataGridView.DataSource into a List
object firstItem = null;
var myDataSource = dataGridView.DataSource;
var myList = ((System.Windows.Forms.BindingSource)dataGridView.DataSource).List;
firstItem = ((System.Collections.IList)myList)[0];
var type = firstItem.GetType();
Type PROJECT1_TYPE = typeof(Project1.SomeClass);
Type PROJECT2_TYPE = typeof(Project2.SomeOtherClass); // many more of these
dynamic newList = null;
if (type.FullName.Equals(PROJECT1_TYPE.FullName))
{
newList = new List<Project1.SomeClass>();
foreach (Project1.SomeClass someClassObject in myList)
{
newList.Add(someClassObject);
}
}
ExcelPackage package = new ExcelPackage();
using ((package)) // use EPPlus
{
// Create the worksheet
ExcelWorksheet worksheet = package.Workbook.Worksheets.Add("Worksheet 1");
// Load the datatable into the sheet, starting from cell A1. Print the column names on row 1
System.Data.DataTable dataTable = new System.Data.DataTable();
dataTable.Columns.Add("Id");
dataTable.Columns.Add("FirstColumn", typeof(string));
dataTable.Columns.Add("SecondColumn", typeof(string));
dataTable.Columns.Add("ThirdColumn", typeof(string));
dataTable.Columns[0].AutoIncrement = true;
var column_id = 0;
foreach (Project1.SomeClass someClassObject in "FirstColumn")
{
DataRow dataRow = dataTable.NewRow();
dataRow["FirstColumn"] = someClassObject.Name;
dataRow["SecondColumn"] = someClassObject.Address;
dataRow["ThirdColumn"] = someClassObject.Phone
dataTable.Rows.Add(dataRow);
column_id += 1;
}
// worksheet is now populated, so save Excel File
...
}

Instead of doing the DataRow creation within this function, you could move it out to the class implementations using a common interface to enforce it, for instance:
public interface DataRowConvertable
{
DataRow GetDataRow();
}
public class SomeClass : DataRowConvertable
{
public SomeClass() { }
public SomeClass(string name, string address, string phone)
{
Name = name;
Address = address;
Phone = phone;
}
public string Name { get; set; }
public string Address { get; set; }
public string Phone { get; set; }
public DataRow GetDataRow()
{
DataRow row = GetDataTable().NewRow();
row["Name"] = this.Name;
row["Address"] = this.Address;
row["Phone"] = this.Phone;
return row;
}
public static DataTable GetDataTable()
{
DataTable table = new DataTable("SomeClassTable");
table.Columns.Add("Name", typeof(string));
table.Columns.Add("Address", typeof(string));
table.Columns.Add("Phone", typeof(string));
return table;
}
}
You could take it further, but this should give you a good alternative and a place to start. You can either leave the GetDataTable function public, and use that as well to create your table instance, or make it private and only use it internally. I would opt for the former and use that in your function to initialize the table before filling it. You could even get rid of the static modifier and add it to your interface, but I prefer the static usage of it in this instance since it is not reliant on the instance of the class and the data involved, only on the structure.
Either way, you could then change the code you have above to look like this:
ExcelWorksheet worksheet = package.Workbook.Worksheets.Add("Worksheet 1");
System.Data.DataTable dataTable = Project1.SomeClass.GetDataTable();
foreach (Project1.SomeClass someClassObject in myList)
{
dataTable.Rows.Add(someClassObject.GetDataRow());
}
If you need an incremented id column, you could easily add that in the GetDataTable/GetDataRow functions and update them just as you were above.
This is just a quick example, it could very likely be cleaned up and optimized some, but it still conveys the idea. Hope it helps you out some.

DataRow Field Cast From Variable

Is it possible to cast a type from a variable? I'm extracting data from a spreadsheet into a class, but because some columns are strings, and others DateTime, I really want a do-all command, that I don't need to map everything manually.
What I have so far:
foreach (PropertyInfo pinfo in asset.GetType().GetProperties())
{
string columnType = (from DataColumn column in data.Columns where column.ColumnName == pinfo.Name select column).First().DataType.ToString();
pinfo.SetValue(asset, row.Field<columnType>(pinfo.Name));
}
At the moment, it doesn't like row.Field<columnType>(), because it's not a real type.
Is it possible to do something like the above, where I'm getting the type contained in a column, and casting this to retrieve the data for that column? I'm in this situation, as I want to retrieve anything using the following statement, regardless of whether it's a string, int or DateTime.
var foo = row.Field<string>("Column Name");
Is there any generic command I can use? Thanks

PropertyInfo.SetValue accepts value as object. If your DataTable has column of appropriate type, then just get column value with row[columnName] which also will be returned as object, and use it to set property value:
foreach (PropertyInfo pinfo in asset.GetType().GetProperties())
{
pinfo.SetValue(asset, row[pinfo.Name]);
}
Sample: consider you have class
public class User
{
public int Id { get; set; }
public string Name { get; set; }
}
And you have DataTable which has columns with appropriate types:
DataTable dt = new DataTable();
dt.Columns.Add("Id", typeof(int));
dt.Columns.Add("Name", typeof(string));
dt.Rows.Add(1, "Bob");
dt.Rows.Add(2, "John");
Then filling user from DataTable will look like:
var user = new User();
var row = dt.Rows[0];
foreach (PropertyInfo pinfo in user.GetType().GetProperties())
pinfo.SetValue(user, row[pinfo.Name]);
NOTE: You can skip properties which don't have appropriate type, also you can handle case when there is no column with property name:
foreach (PropertyInfo pinfo in user.GetType().GetProperties())
{
if (!dt.Columns.Contains(pinfo.Name) ||
dt.Columns[pinfo.Name].DataType != pinfo.PropertyType)
continue;
pinfo.SetValue(user, row[pinfo.Name]);
}

Storing references to an object in DataTable using the "this" keyword

I have a collection of objects with no key or order or other obvious index.
I wish to store data regarding each object in a DataTable. I thought an elegant way of doing this would be to store a reference in the owner column, and make that columns type typeof(MyClass).
However, when I try to do this in practice, it doesn't work (it says the primary keys collide). Turns out that putting the instances into a row field just writes "MyProgram.MyClass" into the field - presumably the output of toString even though that row's type was supposed to be MyClass not string.
Here is some sample code which works in LINQPad:
void Main()
{
// Create a table
var table = new DataTable();
var ownerColumn = new DataColumn("Owner", typeof(MyClass));
var primaryKey = new[] { ownerColumn };
table.Columns.AddRange(primaryKey);
table.PrimaryKey = primaryKey;
table.Columns.Add(new DataColumn("Some Data", typeof(int)) { DefaultValue = 0 });
// Create 2 objects
var c1 = new MyClass();
var c2 = new MyClass();
// Store their data in the table
var row = table.NewRow();
row["Owner"] = c1;
row["Some Data"] = 1;
table.Rows.Add(row);
row = table.NewRow();
row["Owner"] = c2;
row["Some Data"] = 2;
table.Rows.Add(row);
}
// Define other methods and classes here
class MyClass {
}
What do I do to solve this? Do I have to make an id field in MyClass, then use id to fill in the owner column, and then make sure each object receives a unique id at creation myself?

You have to implement System.IComparable (non-generic version) interface on MyClass so that DataTable knows how to to compare the value of the column. If this interface is not defined, the code falls back on comparing object.ToString() results.

You can use auto increment column :
DataTable dTable = new DataTable();
DataColumn auto = new DataColumn("AutoID", typeof(System.Int32));
dTable.Columns.Add(auto);
auto.AutoIncrement = true;
auto.AutoIncrementSeed = 1;
auto.ReadOnly = true;