I have data in a DataReader
which I want to be converted to a List<T>
.
What is a possible simple solution for this?
For e.g. in CustomerEntity class, I have CustomerId and CustomerName properties.If my DataReader returns these two columns as data, then how can I convert it into List<CustomerEntity>
.
This question is related to
c#
datareader
generic-list
I've covered this in a pet project.. use what you want.
Note that the ListEx implements the IDataReader interface.
people = new ListExCommand(command)
.Map(p=> new ContactPerson()
{
Age = p.GetInt32(p.GetOrdinal("Age")),
FirstName = p.GetString(p.GetOrdinal("FirstName")),
IdNumber = p.GetInt64(p.GetOrdinal("IdNumber")),
Surname = p.GetString(p.GetOrdinal("Surname")),
Email = "[email protected]"
})
.ToListEx()
.Where("FirstName", "Peter");
Or use object mapping like in the following example.
people = new ListExAutoMap(personList)
.Map(p => new ContactPerson()
{
Age = p.Age,
FirstName = p.FirstName,
IdNumber = p.IdNumber,
Surname = p.Surname,
Email = "[email protected]"
})
.ToListEx()
.Where(contactPerson => contactPerson.FirstName == "Zack");
Have a look at http://caprisoft.codeplex.com
You cant simply (directly) convert the datareader to list.
You have to loop through all the elements in datareader and insert into list
below the sample code
using (drOutput)
{
System.Collections.Generic.List<CustomerEntity > arrObjects = new System.Collections.Generic.List<CustomerEntity >();
int customerId = drOutput.GetOrdinal("customerId ");
int CustomerName = drOutput.GetOrdinal("CustomerName ");
while (drOutput.Read())
{
CustomerEntity obj=new CustomerEntity ();
obj.customerId = (drOutput[customerId ] != Convert.DBNull) ? drOutput[customerId ].ToString() : null;
obj.CustomerName = (drOutput[CustomerName ] != Convert.DBNull) ? drOutput[CustomerName ].ToString() : null;
arrObjects .Add(obj);
}
}
The simplest Solution :
var dt=new DataTable();
dt.Load(myDataReader);
list<DataRow> dr=dt.AsEnumerable().ToList();
I would (and have) started to use Dapper. To use your example would be like (written from memory):
public List<CustomerEntity> GetCustomerList()
{
using (DbConnection connection = CreateConnection())
{
return connection.Query<CustomerEntity>("procToReturnCustomers", commandType: CommandType.StoredProcedure).ToList();
}
}
CreateConnection()
would handle accessing your db and returning a connection.
Dapper handles mapping datafields to properties automatically. It also supports multiple types and result sets and is very fast.
Query returns IEnumerable
hence the ToList()
.
Obviously @Ian Ringrose
's central thesis that you should be using a library for this is the best single answer here (hence a +1), but for minimal throwaway or demo code here's a concrete illustration of @SLaks
's subtle comment on @Jon Skeet
's more granular (+1'd) answer:
public List<XXX> Load( <<args>> )
{
using ( var connection = CreateConnection() )
using ( var command = Create<<ListXXX>>Command( <<args>>, connection ) )
{
connection.Open();
using ( var reader = command.ExecuteReader() )
return reader.Cast<IDataRecord>()
.Select( x => new XXX( x.GetString( 0 ), x.GetString( 1 ) ) )
.ToList();
}
}
As in @Jon Skeet
's answer, the
.Select( x => new XXX( x.GetString( 0 ), x.GetString( 1 ) ) )
bit can be extracted into a helper (I like to dump them in the query class):
public static XXX FromDataRecord( this IDataRecord record)
{
return new XXX( record.GetString( 0 ), record.GetString( 1 ) );
}
and used as:
.Select( FromDataRecord )
UPDATE Mar 9 13: See also Some excellent further subtle coding techniques to split out the boilerplate in this answer
I would suggest writing an extension method for this:
public static IEnumerable<T> Select<T>(this IDataReader reader,
Func<IDataReader, T> projection)
{
while (reader.Read())
{
yield return projection(reader);
}
}
You can then use LINQ's ToList()
method to convert that into a List<T>
if you want, like this:
using (IDataReader reader = ...)
{
List<Customer> customers = reader.Select(r => new Customer {
CustomerId = r["id"] is DBNull ? null : r["id"].ToString(),
CustomerName = r["name"] is DBNull ? null : r["name"].ToString()
}).ToList();
}
I would actually suggest putting a FromDataReader
method in Customer
(or somewhere else):
public static Customer FromDataReader(IDataReader reader) { ... }
That would leave:
using (IDataReader reader = ...)
{
List<Customer> customers = reader.Select<Customer>(Customer.FromDataReader)
.ToList();
}
(I don't think type inference would work in this case, but I could be wrong...)
I know this question is old, and already answered, but...
Since SqlDataReader already implements IEnumerable, why is there a need to create a loop over the records?
I've been using the method below without any issues, nor without any performance issues: So far I have tested with IList, List(Of T), IEnumerable, IEnumerable(Of T), IQueryable, and IQueryable(Of T)
Imports System.Data.SqlClient
Imports System.Data
Imports System.Threading.Tasks
Public Class DataAccess
Implements IDisposable
#Region " Properties "
''' <summary>
''' Set the Query Type
''' </summary>
''' <value></value>
''' <remarks></remarks>
Public WriteOnly Property QueryType() As CmdType
Set(ByVal value As CmdType)
_QT = value
End Set
End Property
Private _QT As CmdType
''' <summary>
''' Set the query to run
''' </summary>
''' <value></value>
''' <remarks></remarks>
Public WriteOnly Property Query() As String
Set(ByVal value As String)
_Qry = value
End Set
End Property
Private _Qry As String
''' <summary>
''' Set the parameter names
''' </summary>
''' <value></value>
''' <remarks></remarks>
Public WriteOnly Property ParameterNames() As Object
Set(ByVal value As Object)
_PNs = value
End Set
End Property
Private _PNs As Object
''' <summary>
''' Set the parameter values
''' </summary>
''' <value></value>
''' <remarks></remarks>
Public WriteOnly Property ParameterValues() As Object
Set(ByVal value As Object)
_PVs = value
End Set
End Property
Private _PVs As Object
''' <summary>
''' Set the parameter data type
''' </summary>
''' <value></value>
''' <remarks></remarks>
Public WriteOnly Property ParameterDataTypes() As DataType()
Set(ByVal value As DataType())
_DTs = value
End Set
End Property
Private _DTs As DataType()
''' <summary>
''' Check if there are parameters, before setting them
''' </summary>
''' <value></value>
''' <returns></returns>
''' <remarks></remarks>
Private ReadOnly Property AreParams() As Boolean
Get
If (IsArray(_PVs) And IsArray(_PNs)) Then
If (_PVs.GetUpperBound(0) = _PNs.GetUpperBound(0)) Then
Return True
Else
Return False
End If
Else
Return False
End If
End Get
End Property
''' <summary>
''' Set our dynamic connection string
''' </summary>
''' <value></value>
''' <returns></returns>
''' <remarks></remarks>
Private ReadOnly Property _ConnString() As String
Get
If System.Diagnostics.Debugger.IsAttached OrElse My.Settings.AttachToBeta OrElse Not (Common.CheckPaid) Then
Return My.Settings.DevConnString
Else
Return My.Settings.TurboKitsv2ConnectionString
End If
End Get
End Property
Private _Rdr As SqlDataReader
Private _Conn As SqlConnection
Private _Cmd As SqlCommand
#End Region
#Region " Methods "
''' <summary>
''' Fire us up!
''' </summary>
''' <remarks></remarks>
Public Sub New()
Parallel.Invoke(Sub()
_Conn = New SqlConnection(_ConnString)
End Sub,
Sub()
_Cmd = New SqlCommand
End Sub)
End Sub
''' <summary>
''' Get our results
''' </summary>
''' <returns></returns>
''' <remarks></remarks>
Public Function GetResults() As SqlDataReader
Try
Parallel.Invoke(Sub()
If AreParams Then
PrepareParams(_Cmd)
End If
_Cmd.Connection = _Conn
_Cmd.CommandType = _QT
_Cmd.CommandText = _Qry
_Cmd.Connection.Open()
_Rdr = _Cmd.ExecuteReader(CommandBehavior.CloseConnection)
End Sub)
If _Rdr.HasRows Then
Return _Rdr
Else
Return Nothing
End If
Catch sEx As SqlException
Return Nothing
Catch ex As Exception
Return Nothing
End Try
End Function
''' <summary>
''' Prepare our parameters
''' </summary>
''' <param name="objCmd"></param>
''' <remarks></remarks>
Private Sub PrepareParams(ByVal objCmd As Object)
Try
Dim _DataSize As Long
Dim _PCt As Integer = _PVs.GetUpperBound(0)
For i As Long = 0 To _PCt
If IsArray(_DTs) Then
Select Case _DTs(i)
Case 0, 33, 6, 9, 13, 19
_DataSize = 8
Case 1, 3, 7, 10, 12, 21, 22, 23, 25
_DataSize = Len(_PVs(i))
Case 2, 20
_DataSize = 1
Case 5
_DataSize = 17
Case 8, 17, 15
_DataSize = 4
Case 14
_DataSize = 16
Case 31
_DataSize = 3
Case 32
_DataSize = 5
Case 16
_DataSize = 2
Case 15
End Select
objCmd.Parameters.Add(_PNs(i), _DTs(i), _DataSize).Value = _PVs(i)
Else
objCmd.Parameters.AddWithValue(_PNs(i), _PVs(i))
End If
Next
Catch ex As Exception
End Try
End Sub
#End Region
#Region "IDisposable Support"
Private disposedValue As Boolean ' To detect redundant calls
' IDisposable
Protected Overridable Sub Dispose(ByVal disposing As Boolean)
If Not Me.disposedValue Then
If disposing Then
End If
Try
Erase _PNs : Erase _PVs : Erase _DTs
_Qry = String.Empty
_Rdr.Close()
_Rdr.Dispose()
_Cmd.Parameters.Clear()
_Cmd.Connection.Close()
_Conn.Close()
_Cmd.Dispose()
_Conn.Dispose()
Catch ex As Exception
End Try
End If
Me.disposedValue = True
End Sub
' TODO: override Finalize() only if Dispose(ByVal disposing As Boolean) above has code to free unmanaged resources.
Protected Overrides Sub Finalize()
' Do not change this code. Put cleanup code in Dispose(ByVal disposing As Boolean) above.
Dispose(False)
MyBase.Finalize()
End Sub
' This code added by Visual Basic to correctly implement the disposable pattern.
Public Sub Dispose() Implements IDisposable.Dispose
' Do not change this code. Put cleanup code in Dispose(ByVal disposing As Boolean) above.
Dispose(True)
GC.SuppressFinalize(Me)
End Sub
#End Region
End Class
Strong Typing Class
Public Class OrderDCTyping
Public Property OrderID As Long = 0
Public Property OrderTrackingNumber As String = String.Empty
Public Property OrderShipped As Boolean = False
Public Property OrderShippedOn As Date = Nothing
Public Property OrderPaid As Boolean = False
Public Property OrderPaidOn As Date = Nothing
Public Property TransactionID As String
End Class
Usage
Public Function GetCurrentOrders() As IEnumerable(Of OrderDCTyping)
Try
Using db As New DataAccess
With db
.QueryType = CmdType.StoredProcedure
.Query = "[Desktop].[CurrentOrders]"
Using _Results = .GetResults()
If _Results IsNot Nothing Then
_Qry = (From row In _Results.Cast(Of DbDataRecord)()
Select New OrderDCTyping() With {
.OrderID = Common.IsNull(Of Long)(row, 0, 0),
.OrderTrackingNumber = Common.IsNull(Of String)(row, 1, String.Empty),
.OrderShipped = Common.IsNull(Of Boolean)(row, 2, False),
.OrderShippedOn = Common.IsNull(Of Date)(row, 3, Nothing),
.OrderPaid = Common.IsNull(Of Boolean)(row, 4, False),
.OrderPaidOn = Common.IsNull(Of Date)(row, 5, Nothing),
.TransactionID = Common.IsNull(Of String)(row, 6, String.Empty)
}).ToList()
Else
_Qry = Nothing
End If
End Using
Return _Qry
End With
End Using
Catch ex As Exception
Return Nothing
End Try
End Function
I have written the following method using this case.
First, add the namespace: System.Reflection
For Example: T
is return type(ClassName) and dr
is parameter to mapping DataReader
C#, Call mapping method like the following:
List<Person> personList = new List<Person>();
personList = DataReaderMapToList<Person>(dataReaderForPerson);
This is the mapping method:
public static List<T> DataReaderMapToList<T>(IDataReader dr)
{
List<T> list = new List<T>();
T obj = default(T);
while (dr.Read()) {
obj = Activator.CreateInstance<T>();
foreach (PropertyInfo prop in obj.GetType().GetProperties()) {
if (!object.Equals(dr[prop.Name], DBNull.Value)) {
prop.SetValue(obj, dr[prop.Name], null);
}
}
list.Add(obj);
}
return list;
}
VB.NET, Call mapping method like the following:
Dim personList As New List(Of Person)
personList = DataReaderMapToList(Of Person)(dataReaderForPerson)
This is the mapping method:
Public Shared Function DataReaderMapToList(Of T)(ByVal dr As IDataReader) As List(Of T)
Dim list As New List(Of T)
Dim obj As T
While dr.Read()
obj = Activator.CreateInstance(Of T)()
For Each prop As PropertyInfo In obj.GetType().GetProperties()
If Not Object.Equals(dr(prop.Name), DBNull.Value) Then
prop.SetValue(obj, dr(prop.Name), Nothing)
End If
Next
list.Add(obj)
End While
Return list
End Function
Source: Stackoverflow.com