c# - pasar - .NET-Convertir la colección genérica a DataTable

fill list with dataset c#

Question

Estoy tratando de convertir una colección genérica (Lista) en una DataTable. Encontré el siguiente código para ayudarme a hacer esto:

// Sorry about indentation
public class CollectionHelper
{
private CollectionHelper()
{
}
// this is the method I have been using
public static DataTable ConvertTo<T>(IList<T> list)
{
DataTable table = CreateTable<T>();
Type entityType = typeof(T);
PropertyDescriptorCollection properties = TypeDescriptor.GetProperties(entityType);
foreach (T item in list)
{
DataRow row = table.NewRow();
foreach (PropertyDescriptor prop in properties)
{
row[prop.Name] = prop.GetValue(item);
}
table.Rows.Add(row);
}
return table;
}
public static DataTable CreateTable<T>()
{
Type entityType = typeof(T);
DataTable table = new DataTable(entityType.Name);
PropertyDescriptorCollection properties = TypeDescriptor.GetProperties(entityType);
foreach (PropertyDescriptor prop in properties)
{
// HERE IS WHERE THE ERROR IS THROWN FOR NULLABLE TYPES
table.Columns.Add(prop.Name, prop.PropertyType);
}
return table;
}
}

Mi problema es que cuando cambio una de las propiedades de MySimpleClass a un tipo que admite nulos, aparece el siguiente error:

DataSet does not support System.Nullable<>.

¿Cómo puedo hacer esto con propiedades / campos Nullable en mi clase?

Answer 1

Aquí hay una versión con algunas modificaciones para permitir nulos y caracteres ''/ 0'' sin explotar la DataTable.

using System;
using System.Collections;
using System.Collections.Generic;
using System.Reflection;
using System.Data;
namespace SomeNamespace
{
public static class Extenders
{
public static DataTable ToDataTable<T>(this IEnumerable<T> collection, string tableName)
{
DataTable tbl = ToDataTable(collection);
tbl.TableName = tableName;
return tbl;
}
public static DataTable ToDataTable<T>(this IEnumerable<T> collection)
{
DataTable dt = new DataTable();
Type t = typeof(T);
PropertyInfo[] pia = t.GetProperties();
object temp;
DataRow dr;
for (int i = 0; i < pia.Length; i++ )
{
dt.Columns.Add(pia[i].Name, Nullable.GetUnderlyingType(pia[i].PropertyType) ?? pia[i].PropertyType);
dt.Columns[i].AllowDBNull = true;
}
//Populate the table
foreach (T item in collection)
{
dr = dt.NewRow();
dr.BeginEdit();
for (int i = 0; i < pia.Length; i++)
{
temp = pia[i].GetValue(item, null);
if (temp == null || (temp.GetType().Name == "Char" && ((char)temp).Equals(''/0'')))
{
dr[pia[i].Name] = (object)DBNull.Value;
}
else
{
dr[pia[i].Name] = temp;
}
}
dr.EndEdit();
dt.Rows.Add(dr);
}
return dt;
}
}
}

Answer 2

Bien. Dado que DataSet no admite tipos que Nullable.GetUnderlyingType , Nullable.GetUnderlyingType comprobar si la propiedad es un tipo genérico, obtener la definición genérica de ese tipo y luego obtener el argumento (que es el tipo real) utilizando, tal vez, Nullable.GetUnderlyingType . Si el valor es nulo, simplemente use DBNull.Value en el DataSet.

Answer 3

Entonces, presumiblemente, Nullable.GetUnderlyingType a la forma no Nullable.GetUnderlyingType , utilizando Nullable.GetUnderlyingType , y quizás cambie algunos valores null a DbNull.Value ...

Cambia la tarea para ser:

row[prop.Name] = prop.GetValue(item) ?? DBNull.Value;

y al agregar las columnas para ser:

table.Columns.Add(prop.Name, Nullable.GetUnderlyingType(
prop.PropertyType) ?? prop.PropertyType);

Y funciona. ( ?? es el operador nulo-coalescente; utiliza el primer operando si no es nulo, de lo contrario el segundo operando se evalúa y usa)

Answer 4

Sé que esta pregunta es antigua, pero tuve el mismo problema para un método de extensión que hice. Usando la respuesta de Marc Gravell, pude modificar mi código. Este método de extensión manejará listas de tipos primitivos, cadenas, enumeraciones y objetos con propiedades primitivas.

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Linq;
using System.Text;
/// <summary>
/// Converts a List&lt;T&gt; to a DataTable.
/// </summary>
/// <typeparam name="T">The type of the list collection.</typeparam>
/// <param name="list">List instance reference.</param>
/// <returns>A DataTable of the converted list collection.</returns>
public static DataTable ToDataTable<T>(this List<T> list)
{
var entityType = typeof (T);
// Lists of type System.String and System.Enum (which includes enumerations and structs) must be handled differently
// than primitives and custom objects (e.g. an object that is not type System.Object).
if (entityType == typeof (String))
{
var dataTable = new DataTable(entityType.Name);
dataTable.Columns.Add(entityType.Name);
// Iterate through each item in the list. There is only one cell, so use index 0 to set the value.
foreach (T item in list)
{
var row = dataTable.NewRow();
row[0] = item;
dataTable.Rows.Add(row);
}
return dataTable;
}
else if (entityType.BaseType == typeof (Enum))
{
var dataTable = new DataTable(entityType.Name);
dataTable.Columns.Add(entityType.Name);
// Iterate through each item in the list. There is only one cell, so use index 0 to set the value.
foreach (string namedConstant in Enum.GetNames(entityType))
{
var row = dataTable.NewRow();
row[0] = namedConstant;
dataTable.Rows.Add(row);
}
return dataTable;
}
// Check if the type of the list is a primitive type or not. Note that if the type of the list is a custom
// object (e.g. an object that is not type System.Object), the underlying type will be null.
var underlyingType = Nullable.GetUnderlyingType(entityType);
var primitiveTypes = new List<Type>
{
typeof (Byte),
typeof (Char),
typeof (Decimal),
typeof (Double),
typeof (Int16),
typeof (Int32),
typeof (Int64),
typeof (SByte),
typeof (Single),
typeof (UInt16),
typeof (UInt32),
typeof (UInt64),
};
var typeIsPrimitive = primitiveTypes.Contains(underlyingType);
// If the type of the list is a primitive, perform a simple conversion.
// Otherwise, map the object''s properties to columns and fill the cells with the properties'' values.
if (typeIsPrimitive)
{
var dataTable = new DataTable(underlyingType.Name);
dataTable.Columns.Add(underlyingType.Name);
// Iterate through each item in the list. There is only one cell, so use index 0 to set the value.
foreach (T item in list)
{
var row = dataTable.NewRow();
row[0] = item;
dataTable.Rows.Add(row);
}
return dataTable;
}
else
{
// TODO:
// 1. Convert lists of type System.Object to a data table.
// 2. Handle objects with nested objects (make the column name the name of the object and print "system.object" as the value).
var dataTable = new DataTable(entityType.Name);
var propertyDescriptorCollection = TypeDescriptor.GetProperties(entityType);
// Iterate through each property in the object and add that property name as a new column in the data table.
foreach (PropertyDescriptor propertyDescriptor in propertyDescriptorCollection)
{
// Data tables cannot have nullable columns. The cells can have null values, but the actual columns themselves cannot be nullable.
// Therefore, if the current property type is nullable, use the underlying type (e.g. if the type is a nullable int, use int).
var propertyType = Nullable.GetUnderlyingType(propertyDescriptor.PropertyType) ?? propertyDescriptor.PropertyType;
dataTable.Columns.Add(propertyDescriptor.Name, propertyType);
}
// Iterate through each object in the list adn add a new row in the data table.
// Then iterate through each property in the object and add the property''s value to the current cell.
// Once all properties in the current object have been used, add the row to the data table.
foreach (T item in list)
{
var row = dataTable.NewRow();
foreach (PropertyDescriptor propertyDescriptor in propertyDescriptorCollection)
{
var value = propertyDescriptor.GetValue(item);
row[propertyDescriptor.Name] = value ?? DBNull.Value;
}
dataTable.Rows.Add(row);
}
return dataTable;
}
}

Answer 5

Si Nullable.GetUnderlyingType() dado su prop.PropertyType devuelve un valor no nulo, utilícelo como el tipo de una columna. De lo contrario, use prop.PropertyType sí mismo.