5

我需要将此 LINQ to Entities 查询(如下)返回的数据存储到 DataTable 中,以便可以将其用作 DataGridView 的数据源,我该怎么做?

在这种情况下,我使用 LINQ to Entities 来查询实体框架概念模型,db继承自System.Data.Entity.DbContext.

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;
}

我尝试过这样做(如下),但它在执行期间引发了异常 [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

4

3 回答 3

2

这里有一件重要的事情,IEnumerable<DataRow>当您选择 时,您将 Linq 查询转换为 ( ) vendedor,所以我假设供应商是 的一个实例Vendedor,因此您的查询将返回一个IEnumerable<Vendedor>

那应该可以解决您的问题,但是,您可以尝试使用生成的 DataTable 作为 DataGridView 的 DataSource 吗?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;

希望我能帮上忙!

编辑

作为一个侧面(非常个人)的说明,您可以尝试在您的选择上使用 lambda,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;

干净多了,你不觉得吗?

编辑 2 我刚刚意识到您在 CopyToDataTable 上所说的仅适用于 DataRow,所以最后一个(诚然不是那么干净)的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,要考虑的事情

  • 此解决方案不适用于复杂的属性
  • 自定义结果表可能有点棘手

虽然这可能会解决问题,但我认为这不是一个很好的方法,但这可能是一个不错的想法的开始:)

希望这次能帮上忙!

于 2013-08-25T23:33:05.237 回答
0

这是MSDN推荐的解决方案:https ://msdn.microsoft.com/en-us/library/bb669096(v=vs.110).aspx

我已经成功地实现了它(*为处理可为空的 DateTime 进行了少量添加。)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**昂贵**并且您必须在错误处理中对其进行自定义。

于 2016-08-10T21:29:00.897 回答
-2

你可以把

var 查询 = 从 ....

this.dataGridViewProcura.DataSource = 查询。列表()

于 2014-05-01T01:17:10.577 回答