如何将DataTable转换为通用列表？-Java 学习之路

156

目前，我正在使用：

DataTable dt = CreateDataTableInSomeWay();

List<DataRow> list = new List<DataRow>(); 
foreach (DataRow dr in dt.Rows)
{
    list.Add(dr);
}

有更好的/神奇的方式吗？

21 回答

using System.Data;


var myEnumerable = myDataTable.AsEnumerable();

List<MyClass> myClassList =
    (from item in myEnumerable
     select new MyClass{
         MyClassProperty1 = item.Field<string>("DataTableColumnName1"),
         MyClassProperty2 = item.Field<string>("DataTableColumnName2")
    }).ToList();

回复于 2024-04-28T03:29:28+08:00

6
再次使用3.5你可以这样做：
```
dt.Select().ToList()
```
BRGDS
回复于 2024-04-28T03:29:28+08:00
3
如果您使用的是.NET 3.5，则可以使用DataTableExtensions.AsEnumerable（扩展方法）然后如果您确实需要 List<DataRow> 而不仅仅是 IEnumerable<DataRow> ，则可以调用Enumerable.ToList：
```
IEnumerable<DataRow> sequence = dt.AsEnumerable();
```
要么
```
using System.Linq;
...
List<DataRow> list = dt.AsEnumerable().ToList();
```
回复于 2024-04-28T03:29:28+08:00

List<Employee> emp = new List<Employee>();

//Maintaining DataTable on ViewState
//For Demo only

DataTable dt = ViewState["CurrentEmp"] as DataTable;

//read data from DataTable 
//using lamdaexpression


emp = (from DataRow row in dt.Rows

   select new Employee
   {
       _FirstName = row["FirstName"].ToString(),
       _LastName = row["Last_Name"].ToString()

   }).ToList();

回复于 2024-04-28T03:29:28+08:00

3
使用C＃3.0和System.Data.DataSetExtensions.dll，
```
List<DataRow> rows = table.Rows.Cast<DataRow>().ToList();
```
回复于 2024-04-28T03:29:28+08:00
4
你可以用
```
List<DataRow> list = new List<DataRow>(dt.Select());
```
dt.Select() 将返回表中的所有行，作为数据行数组， List 构造函数接受该对象数组作为参数，以便最初填充列表 .
回复于 2024-04-28T03:29:28+08:00
30
如果您只想要返回“ID”int字段中的值列表，您可以使用...
```
List<int> ids = (from row in dt.AsEnumerable() select Convert.ToInt32(row["ID"])).ToList();
```
回复于 2024-04-28T03:29:28+08:00

您可以创建扩展功能：

public static List<T> ToListof<T>(this DataTable dt)
{
    const BindingFlags flags = BindingFlags.Public | BindingFlags.Instance;
    var columnNames = dt.Columns.Cast<DataColumn>()
        .Select(c => c.ColumnName)
        .ToList();
    var objectProperties = typeof(T).GetProperties(flags);
    var targetList = dt.AsEnumerable().Select(dataRow =>
    {
        var instanceOfT = Activator.CreateInstance<T>();

        foreach (var properties in objectProperties.Where(properties => columnNames.Contains(properties.Name) && dataRow[properties.Name] != DBNull.Value))
        {
            properties.SetValue(instanceOfT, dataRow[properties.Name], null);
        }
        return instanceOfT;
    }).ToList();

    return targetList;
}


var output = yourDataInstance.ToListof<targetModelType>();

回复于 2024-04-28T03:29:28+08:00

244

我已经从这个答案添加了一些修改（https://stackoverflow.com/a/24588210/4489664），因为对于可以为空的类型，它将返回异常

public static List<T> DataTableToList<T>(this DataTable table) where T: new()
{
    List<T> list = new List<T>();
    var typeProperties = typeof(T).GetProperties().Select(propertyInfo => new
        {
            PropertyInfo = propertyInfo,
            Type = Nullable.GetUnderlyingType(propertyInfo.PropertyType) ?? propertyInfo.PropertyType
        }).ToList();

    foreach (var row in table.Rows.Cast<DataRow>())
    {
        T obj = new T();
        foreach (var typeProperty in typeProperties)
        {
            object value = row[typeProperty.PropertyInfo.Name];
            object safeValue = value == null || DBNull.Value.Equals(value)
                ? null
                : Convert.ChangeType(value, typeProperty.Type);

            typeProperty.PropertyInfo.SetValue(obj, safeValue, null);
        }
        list.Add(obj);
    }
    return list;
}

回复于 2024-04-28T03:29:28+08:00

34
一种更“神奇”的方式，不需要.NET 3.5 .

例如，如果 DBDatatable 返回单个Guids列（SQL中的uniqueidentifier），那么您可以使用：
```
Dim gList As New List(Of Guid)
gList.AddRange(DirectCast(DBDataTable.Select(), IEnumerable(Of Guid)))
```
回复于 2024-04-28T03:29:28+08:00

// this is better suited for expensive object creation/initialization
IEnumerable<Employee> ParseEmployeeTable(DataTable dtEmployees)
{
    var employees = new ConcurrentBag<Employee>();

    Parallel.ForEach(dtEmployees.AsEnumerable(), (dr) =>
    {
        employees.Add(new Employee() 
        {
            _FirstName = dr["FirstName"].ToString(),
            _LastName = dr["Last_Name"].ToString()
        });
    });

    return employees;
}

回复于 2024-04-28T03:29:28+08:00

0

DataTable.Select() 并不按照它们在数据表中的顺序给出行 .

如果顺序很重要，我觉得迭代datarow集合并形成List是正确的方法，或者你也可以使用 DataTable.Select(string filterexpression, string sort) 的重载 .

但是这个重载可能无法处理SQL提供的所有排序（如逐个...） .

回复于 2024-04-28T03:29:28+08:00
0
这是一个DataTable扩展方法，它将DataTable转换为通用列表 .

https://gist.github.com/gaui/a0a615029f1327296cf8

Usage:
```
List<Employee> emp = dtTable.DataTableToList<Employee>();
```
回复于 2024-04-28T03:29:28+08:00

DataTable dt;   // datatable should contains datacolumns with Id,Name

List<Employee> employeeList=new List<Employee>();  // Employee should contain  EmployeeId, EmployeeName as properties

foreach (DataRow dr in dt.Rows)
{
    employeeList.Add(new Employee{EmployeeId=dr.Id,EmplooyeeName=dr.Name});
}

回复于 2024-04-28T03:29:28+08:00

/* This is a generic method that will convert any type of DataTable to a List 
         * 
         * 
         * Example :    List< Student > studentDetails = new List< Student >();  
         *              studentDetails = ConvertDataTable< Student >(dt);  
         *
         * Warning : In this case the DataTable column's name and class property name
         *           should be the same otherwise this function will not work properly
         */

以下是两个函数，如果我们传递DataTable和用户定义的类 . 然后它将使用DataTable数据返回该类的List .

public static List<T> ConvertDataTable<T>(DataTable dt)
        {
            List<T> data = new List<T>();
            foreach (DataRow row in dt.Rows)
            {
                T item = GetItem<T>(row);
                data.Add(item);
            }
            return data;
        }


        private static T GetItem<T>(DataRow dr)
        {
            Type temp = typeof(T);
            T obj = Activator.CreateInstance<T>();

            foreach (DataColumn column in dr.Table.Columns)
            {
                foreach (PropertyInfo pro in temp.GetProperties())
                {
                   //in case you have a enum/GUID datatype in your model
                   //We will check field's dataType, and convert the value in it.
                    if (pro.Name == column.ColumnName){                
                    try
                    {
                        var convertedValue = GetValueByDataType(pro.PropertyType, dr[column.ColumnName]);
                        pro.SetValue(obj, convertedValue, null);
                    }
                    catch (Exception e)
                    {         
                       //ex handle code                   
                        throw;
                    }
                        //pro.SetValue(obj, dr[column.ColumnName], null);
                }
                    else
                        continue;
                }
            }
            return obj;
        }

此方法将检查字段的数据类型，并将dataTable值转换为该数据类型 .

private static object GetValueByDataType(Type propertyType, object o)
    {
        if (o.ToString() == "null")
        {
            return null;
        }
        if (propertyType == (typeof(Guid)) || propertyType == typeof(Guid?))
        {
            return Guid.Parse(o.ToString());
        }
        else if (propertyType == typeof(int) || propertyType.IsEnum) 
        {
            return Convert.ToInt32(o);
        }
        else if (propertyType == typeof(decimal) )
        {
            return Convert.ToDecimal(o);
        }
        else if (propertyType == typeof(long))
        {
            return Convert.ToInt64(o);
        }
        else if (propertyType == typeof(bool) || propertyType == typeof(bool?))
        {
            return Convert.ToBoolean(o);
        }
        else if (propertyType == typeof(DateTime) || propertyType == typeof(DateTime?))
        {
            return Convert.ToDateTime(o);
        }
        return o.ToString();
    }

要调用上述方法，请使用以下语法：

List< Student > studentDetails = new List< Student >();  
studentDetails = ConvertDataTable< Student >(dt);

根据您的要求更改学生 class 名称和学生值 . 在这种情况下，DataTable列的名称和类属性名称应该相同，否则此函数将无法正常工作 .

回复于 2024-04-28T03:29:28+08:00

This worked for me: 至少需要.Net Framework 3.5，下面的代码显示DataRow转向Generic.IEnumerable，comboBox1已用于更好的说明 .

using System.Linq;

DataTable dt = new DataTable();            
dt = myClass.myMethod();                 
List<object> list = (from row in dt.AsEnumerable() select (row["name"])).ToList();
comboBox1.DataSource = list;

回复于 2024-04-28T03:29:28+08:00

0

使用 System.Data 命名空间然后你会得到 .AsEnumerable() .

回复于 2024-04-28T03:29:28+08:00

Output

public class ModelUser
{
    #region Model

    private string _username;
    private string _userpassword;
    private string _useremail;
    private int _userid;

    /// <summary>
    /// 
    /// </summary>
    public int userid
    {
        set { _userid = value; }
        get { return _userid; }
    }


    /// <summary>
    /// 
    /// </summary>

    public string username
    {
        set { _username = value; }
        get { return _username; }
    }

    /// <summary>
    /// 
    /// </summary>
    public string useremail
    {
        set { _useremail = value; }
        get { return _useremail; }
    }

    /// <summary>
    /// 
    /// </summary>
    public string userpassword
    {
        set { _userpassword = value; }
        get { return _userpassword; }
    }
    #endregion Model
}

public List<ModelUser> DataTableToList(DataTable dt)
{
    List<ModelUser> modelList = new List<ModelUser>();
    int rowsCount = dt.Rows.Count;
    if (rowsCount > 0)
    {
        ModelUser model;
        for (int n = 0; n < rowsCount; n++)
        {
            model = new ModelUser();

            model.userid = (int)dt.Rows[n]["userid"];
            model.username = dt.Rows[n]["username"].ToString();
            model.useremail = dt.Rows[n]["useremail"].ToString();
            model.userpassword = dt.Rows[n]["userpassword"].ToString();

            modelList.Add(model);
        }
    }
    return modelList;
}

static DataTable GetTable()
{
    // Here we create a DataTable with four columns.
    DataTable table = new DataTable();
    table.Columns.Add("userid", typeof(int));
    table.Columns.Add("username", typeof(string));
    table.Columns.Add("useremail", typeof(string));
    table.Columns.Add("userpassword", typeof(string));

    // Here we add five DataRows.
    table.Rows.Add(25, "Jame", "Jame@hotmail.com", DateTime.Now.ToString());
    table.Rows.Add(50, "luci", "luci@hotmail.com", DateTime.Now.ToString());
    table.Rows.Add(10, "Andrey", "Andrey@hotmail.com", DateTime.Now.ToString());
    table.Rows.Add(21, "Michael", "Michael@hotmail.com", DateTime.Now.ToString());
    table.Rows.Add(100, "Steven", "Steven@hotmail.com", DateTime.Now.ToString());
    return table;
}

protected void Page_Load(object sender, EventArgs e)
{
    List<ModelUser> userList = new List<ModelUser>();

    DataTable dt = GetTable();

    userList = DataTableToList(dt);

    gv.DataSource = userList;
    gv.DataBind();
}[enter image description here][1]

</asp:GridView>
</div>

回复于 2024-04-28T03:29:28+08:00

我们可以使用通用方法将 DataTable 转换为 List ，而不是手动将 DataTable 转换为 List .

注意： DataTable 的 ColumnName 和 Type 的 PropertyName 应该相同 .

调用以下方法：

long result = Utilities.ConvertTo<Student>(dt ,out listStudent);

// Generic Method
public class Utilities
{
    public static long ConvertTo<T>(DataTable table, out List<T> entity)
    {
        long returnCode = -1;
        entity = null;

        if (table == null)
        {
            return -1;
        }

        try
        {
            entity = ConvertTo<T>(table.Rows);
            returnCode = 0;
        }

        catch (Exception ex)
        {
            returnCode = 1000;
        }

        return returnCode;
    }

    static List<T> ConvertTo<T>(DataRowCollection rows)
    {
        List<T> list = null;
        if (rows != null)
        {
            list = new List<T>();

            foreach (DataRow row in rows)
            {
                T item = CreateItem<T>(row);
                list.Add(item);
            }
        }

        return list;
    }

    static T CreateItem<T>(DataRow row)
    {
        string str = string.Empty;
        string strObj = string.Empty;

        T obj = default(T);

        if (row != null)
        {
            obj = Activator.CreateInstance<T>();
            strObj = obj.ToString();
            NameValueCollection objDictionary = new NameValueCollection();

            foreach (DataColumn column in row.Table.Columns)
            {
                PropertyInfo prop = obj.GetType().GetProperty(column.ColumnName);

                if (prop != null)
                {
                    str = column.ColumnName;

                    try
                    {
                        objDictionary.Add(str, row[str].ToString());
                        object value = row[column.ColumnName];
                        Type vType = obj.GetType();

                        if (value == DBNull.Value)
                        {
                            if (vType == typeof(int) || vType == typeof(Int16)
                                                     || vType == typeof(Int32)
                                                     || vType == typeof(Int64)
                                                     || vType == typeof(decimal)
                                                     || vType == typeof(float)
                                                     || vType == typeof(double))
                            {
                                value = 0;
                            }

                            else if (vType == typeof(bool))
                            {
                                value = false;
                            }

                            else if (vType == typeof(DateTime))
                            {
                                value = DateTime.MaxValue;
                            }

                            else
                            {
                                value = null;
                            }

                            prop.SetValue(obj, value, null);
                        }

                        else
                        {
                            prop.SetValue(obj, value, null);
                        }
                    }

                    catch(Exception ex)
                    {

                    }
                }
            }

            PropertyInfo ActionProp = obj.GetType().GetProperty("ActionTemplateValue");

            if (ActionProp != null)
            {
                object ActionValue = objDictionary;
                ActionProp.SetValue(obj, ActionValue, null);
            }
        }

        return obj;
    }
}

回复于 2024-04-28T03:29:28+08:00

61
https://www.nuget.org/packages/AD.GenericConversion/

查看此库以进行转换，您将在此处找到所有类型的转换，例如： -
- DataTable到GenericList
- DataTable的通用类型
- Json到DataTable，通用列表，通用类型
- DataTable到Json
回复于 2024-04-28T03:29:28+08:00

您可以使用类似于通用列表的数据通用方法

public static List<T> DataTableToList<T>(this DataTable table) where T : class, new()
{
    try
    {
        List<T> list = new List<T>();

        foreach (var row in table.AsEnumerable())
        {
            T obj = new T();

            foreach (var prop in obj.GetType().GetProperties())
            {
                try
                {
                    PropertyInfo propertyInfo = obj.GetType().GetProperty(prop.Name);
                    if (propertyInfo.PropertyType.IsEnum)
                    {
                        propertyInfo.SetValue(obj, Enum.Parse(propertyInfo.PropertyType, row[prop.Name].ToString()));
                    }
                    else
                    {
                        propertyInfo.SetValue(obj, Convert.ChangeType(row[prop.Name], propertyInfo.PropertyType), null);
                    }                          
                }
                catch
                {
                    continue;
                }
            }

            list.Add(obj);
        }

        return list;
    }
    catch
    {
        return null;
    }
}

回复于 2024-04-28T03:29:28+08:00

如何将DataTable转换为通用列表？

21 回答

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