我需要将从这个LINQ返回的实体查询（下面）返回的数据存储到DataTable中，以便我可以将它用作DataGridView的数据源，我该怎么做？
在这种情况下，我使用LINQ to Entities来查询Entity Framework概念模型，因此db是一个继承自System.Data.Entity.DbContext的类。
using (TccContext db = new TccContext())
{
var query = from vendedor in db.Vendedores.AsEnumerable()
where vendedor.codigo == Convert.ToInt32(textBoxPesquisa.Text)
select vendedor;
// I'd like to do something like DataTable dt = query;
}
我试图这样做（下面），但它在执行期间抛出异常[1]。
using (TccContext db = new TccContext())
{
IEnumerable<DataRow> query = (IEnumerable<DataRow>)(from vendedor in db.Vendedores.AsEnumerable()
where vendedor.codigo == Convert.ToInt32(textBoxPesquisa.Text)
select vendedor);
using (DataTable dt = query.CopyToDataTable<DataRow>())
{
this.dataGridViewProcura.Rows.Add(
dt.Rows[0][0], // Código
dt.Rows[0][1], // Nome
dt.Rows[0][2]); // Venda Mensal
}
}
[1]：例外：InvalidCastException
Unable to cast object of type 'WhereEnumerableIterator`1[Projeto_TCC.Models.Vendedor]' to type 'System.Collections.Generic.IEnumerable`1[System.Data.DataRow]'.
提前致谢
答案 0 :(得分：2)
这里有一件重要的事情，当您选择IEnumerable<DataRow>时，您将Linq查询转换为（vendedor），因此我假设vendedor是Vendedor的实例，因此，您的查询将返回IEnumerable<Vendedor>
这应该可以解决您的问题，但是，您是否可以尝试将生成的DataTable用作DataGridView的DataSource？它会是这样的：
var query = (from vendedor in db.Vendedores.AsEnumerable()
where vendedor.codigo == Convert.ToInt32(textBoxPesquisa.Text)
select vendedor);
var dt = query.CopyToDataTable<Vendedor>();
this.dataGridViewProcura.DataSource = dt;
希望我能帮忙！
修改
作为一个侧面（非常个人化）的注释，你可以尝试在你的选择上使用lambdas，它们看起来更漂亮：）
var pesquisa = Convert.ToInt32(textBoxPesquisa.Text);
var query = db.Vendedores.Where(vendedor => vendedor.codigo == pesquisa);
var dt = query.CopyToDataTable<Vendedor>();
this.dataGridViewProcura.DataSource = dt;
更清洁，你不觉得吗？
编辑2 我刚刚意识到你在CopyToDataTable上所说的只是DataRow，所以最后（当然不是那么干净）解决方案是模仿助手上的逻辑？
public DataTable CopyGenericToDataTable<T>(this IEnumerable<T> items)
{
var properties = typeof(T).GetProperties();
var result = new DataTable();
//Build the columns
foreach ( var prop in properties ) {
result.Columns.Add(prop.Name, prop.PropertyType);
}
//Fill the DataTable
foreach( var item in items ){
var row = result.NewRow();
foreach ( var prop in properties ) {
var itemValue = prop.GetValue(item, new object[] {});
row[prop.Name] = itemValue;
}
result.Rows.Add(row);
}
return result;
}
现在，需要考虑的事项：
虽然这可能会解决问题，但我认为这不是一个很好的方法，但它可能是一个不错的想法的开始：）
我希望这次可以帮忙！
答案 1 :(得分：0)
这是 MSDN 推荐的解决方案：https://msdn.microsoft.com/en-us/library/bb669096(v=vs.110).aspx
我已经成功实施了它 （*添加少量可处理可为空的DateTime。） 如下：
using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Data;
using System.Reflection;
/// <summary>
/// Converts Entity Type to DataTable
/// </summary>
public class ObjectShredder<T>
{
private System.Reflection.FieldInfo[] _fi;
private System.Reflection.PropertyInfo[] _pi;
private System.Collections.Generic.Dictionary<string, int> _ordinalMap;
private System.Type _type;
// ObjectShredder constructor.
public ObjectShredder()
{
_type = typeof(T);
_fi = _type.GetFields();
_pi = _type.GetProperties();
_ordinalMap = new Dictionary<string, int>();
}
/// <summary>
/// Loads a DataTable from a sequence of objects.
/// </summary>
/// <param name="source">The sequence of objects to load into the DataTable.</param>
/// <param name="table">The input table. The schema of the table must match that
/// the type T. If the table is null, a new table is created with a schema
/// created from the public properties and fields of the type T.</param>
/// <param name="options">Specifies how values from the source sequence will be applied to
/// existing rows in the table.</param>
/// <returns>A DataTable created from the source sequence.</returns>
public DataTable Shred(IEnumerable<T> source, DataTable table, LoadOption? options)
{
// Load the table from the scalar sequence if T is a primitive type.
if (typeof(T).IsPrimitive)
{
return ShredPrimitive(source, table, options);
}
// Create a new table if the input table is null.
if (table == null)
{
table = new DataTable(typeof(T).Name);
}
// Initialize the ordinal map and extend the table schema based on type T.
table = ExtendTable(table, typeof(T));
// Enumerate the source sequence and load the object values into rows.
table.BeginLoadData();
using (IEnumerator<T> e = source.GetEnumerator())
{
while (e.MoveNext())
{
if (options != null)
{
table.LoadDataRow(ShredObject(table, e.Current), (LoadOption)options);
}
else
{
table.LoadDataRow(ShredObject(table, e.Current), true);
}
}
}
table.EndLoadData();
// Return the table.
return table;
}
public DataTable ShredPrimitive(IEnumerable<T> source, DataTable table, LoadOption? options)
{
// Create a new table if the input table is null.
if (table == null)
{
table = new DataTable(typeof(T).Name);
}
if (!table.Columns.Contains("Value"))
{
table.Columns.Add("Value", typeof(T));
}
// Enumerate the source sequence and load the scalar values into rows.
table.BeginLoadData();
using (IEnumerator<T> e = source.GetEnumerator())
{
Object[] values = new object[table.Columns.Count];
while (e.MoveNext())
{
values[table.Columns["Value"].Ordinal] = e.Current;
if (options != null)
{
table.LoadDataRow(values, (LoadOption)options);
}
else
{
table.LoadDataRow(values, true);
}
}
}
table.EndLoadData();
// Return the table.
return table;
}
public object[] ShredObject(DataTable table, T instance)
{
FieldInfo[] fi = _fi;
PropertyInfo[] pi = _pi;
if (instance.GetType() != typeof(T))
{
// If the instance is derived from T, extend the table schema
// and get the properties and fields.
ExtendTable(table, instance.GetType());
fi = instance.GetType().GetFields();
pi = instance.GetType().GetProperties();
}
// Add the property and field values of the instance to an array.
Object[] values = new object[table.Columns.Count];
foreach (FieldInfo f in fi)
{
values[_ordinalMap[f.Name]] = f.GetValue(instance);
}
foreach (PropertyInfo p in pi)
{
values[_ordinalMap[p.Name]] = p.GetValue(instance, null);
}
// Return the property and field values of the instance.
return values;
}
public DataTable ExtendTable(DataTable table, Type type)
{
// Extend the table schema if the input table was null or if the value
// in the sequence is derived from type T.
foreach (FieldInfo f in type.GetFields())
{
if (!_ordinalMap.ContainsKey(f.Name))
{
// Add the field as a column in the table if it doesn't exist
// already.
DataColumn dc = table.Columns.Contains(f.Name) ? table.Columns[f.Name]
: table.Columns.Add(f.Name, f.FieldType);
// Add the field to the ordinal map.
_ordinalMap.Add(f.Name, dc.Ordinal);
}
}
foreach (PropertyInfo p in type.GetProperties())
{
if (!_ordinalMap.ContainsKey(p.Name))
{
// Add the property as a column in the table if it doesn't exist already.
DataColumn dc = table.Columns[p.Name];
//Added Try Catch to account for Nullable Types
try
{
dc = table.Columns.Contains(p.Name) ? table.Columns[p.Name]
: table.Columns.Add(p.Name, p.PropertyType);
}
catch (NotSupportedException nsEx)
{
string pType = p.PropertyType.ToString();
dc = pType.Contains("System.DateTime") ? table.Columns.Add(p.Name, typeof(System.DateTime)) : table.Columns.Add(p.Name);
//dc = table.Columns.Add(p.Name); //Modified to above statment in order to accomodate Nullable date Time
}
// Add the property to the ordinal map.
_ordinalMap.Add(p.Name, dc.Ordinal);
}
}
// Return the table.
return table;
}
}
}
这个解决方案的（大）警告是**价格昂贵**你必须在错误处理中自定义它。
答案 2 :(得分：-2)
你可以把
var query = from ....
this.dataGridViewProcura.DataSource = query。 tolist（）