LINQ to Entities查询到DataTable

Question

我需要将从此LINQ返回的数据存储到实体查询（下面）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来针对实体框架概念模型进行查询，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; 
} 

我试过这样做（下面），但它在执行过程中会引发异常[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]：异常：InvalidCastException

Unable to cast object of type 'WhereEnumerableIterator`1[Projeto_TCC.Models.Vendedor]' to type 'System.Collections.Generic.IEnumerable`1[System.Data.DataRow]'. 

在此先感谢

Answer 1

这里有一个重要的事情，你是铸造你的LINQ查询（IEnumerable<DataRow>）当你选择vendedor，所以我认为vendedor是Vendedor的一个实例，所以你的查询将返回一个IEnumerable<Vendedor>

这应该解决您的问题，而且，您是否可以尝试将生成的DataTable用作DataGridView的DataSource？这将是这样的：

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; 

希望我能帮助！

编辑

作为一个方面（和非常个人化）注意，你可以尝试使用您选择的lambda表达式，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; 

会更加清晰，你不认为？

EDIT 2 我刚刚意识到你说的对CopyToDataTable是对的DataRow而已，所以最后的（当然不那么干净）解决方案是模仿助手中的逻辑是什么？现在

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; 
} 

，事情要考虑：

• 该解决方案不会复杂性
• 自定义生成的表的工作可能是一个有点棘手

虽然这可能会解决这个问题，我不认为这是一个很好的方法，但它合作这是一个不错的想法:)

我希望我能帮助这次！

Answer 2

你可以把

VAR的查询=从....

this.dataGridViewProcura.DataSource =查询。tolist（）

Answer 3

这是一个在MSDN推荐的解决方案：（。*轻微增加处理可空的DateTime）https://msdn.microsoft.com/en-us/library/bb669096(v=vs.110).aspx

我已经实现了它成功 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）警告是它是** co狡猾的**，你必须在错误处理中定制它。