LINQ匿名类型+ MVC视图
https://stackoverflow.com/questions/410073
-
03-07-2019 - |
italiano
english
français
española
中国
日本の
العربية
Deutsch
한국어
Português
Russian题
我已经看到很多关于此的问题，但我从来没有真正得到我需要的答案。
我正在将一个相当大的Web应用程序从Web Forms转换为MVC，过了一段时间我将数据传递给视图时遇到了问题。在Action中我执行代码：
//This is just an example
ViewData["QProducts"] = from p in db.Products select new{Name = p.Name, Date = p.ToShortDateString() }
ViewData["QUsers"] = from u in db.Users select u;
我使用foreach循环迭代html中的对象，如下所示：
foreach(var q in (IEnumerable)ViewData["QEvents"])
{
/*Print the data here*/
}
在使用MVC之前我只使用了一个asp:Repeater，但由于这是MVC，我无法使用ASP.NET控件。
我应该如何将此数据传递给View？我真的没有选择不在这里使用匿名类型。 <%#ViewData.Eval()%>显然不行。
任何想法？
解决方案
而不是匿名类型，创建一个类型来保存名称和日期：
public class NameDate
{
public string Name { get; set; }
public DateTime Date { get; set; }
}
然后在Linq查询中使用它：
from p in db.Products select new NameDate { Name = p.Name, Date = p.Date }
强烈键入您的视图MyView<IEnumerable<NameDate>>，然后只需执行foreach ( var nameDate in ViewData.Model )...
其他提示
如果你感觉有点懒，你可以在这里使用这段代码......它有点长，但基本上它是反射的包装......
var something = { Name = "Jim", Age = 25 };
AnonymousType type = AnonymousType.Create(something);
//then used...
string name = type.Get<string>("Name");
int age = type.Get<int>("Age", -1 /* optional default value */);
这是代码......
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Reflection;
namespace Code {
/// <summary>
/// A convenient method of accessing the values of an
/// anonymous type without needing to define a separate class
/// </summary>
public class AnonymousType {
#region Constants
private const string EXCEPTION_MISSING_PARAMETER_INFORMATION =
"Unable to match the parameter '{0}' to a property in the AnonymousType. This could be due to a casting problem or a Property that does not exist.";
private const string EXCEPTION_COULD_NOT_ACCESS_FIELD =
"Unable to find a field named '{0}' (of type {1})";
private const string EXCEPTION_COULD_NOT_ACCESS_FIELD_AT_INDEX =
"Unable to find a field named '{0}' at the requested index (of type {1})";
#endregion
#region Constructors
/// <summary>
/// Creates a new AutoType for methods that return Anonymus types
/// </summary>
public AnonymousType(object type) {
this._Init(type, false);
}
/// <summary>
/// Creates a new AutoType for methods that return Anonymus types and
/// detetrmins if exceptions should be thrown if a type is missing
/// </summary>
public AnonymousType(object type, bool supressErrors) {
this._Init(type, supressErrors);
}
/// <summary>
/// Initalizes the data for the is type
/// </summary>
private void _Init(object type, bool supressErrors) {
this.SupressExceptions = supressErrors;
this.m_Type = type.GetType();
this.m_TypeData = type;
}
#endregion
#region Static Routines
/// <summary>
/// Creates a new Anonymous Type from the provided object data
/// </summary>
public static AnonymousType Create(object data) {
return new AnonymousType(data);
}
/// <summary>
/// Creates a new Anonymous Type from the provided object data
/// </summary>
public static AnonymousType Create(object data, bool supressErrors) {
return new AnonymousType(data, supressErrors);
}
#endregion
#region Private Members
/// <summary>
/// The type that will be accessed via reflection
/// </summary>
private Type m_Type;
/// <summary>
/// The actual typs that is being used
/// </summary>
private object m_TypeData;
#endregion
#region Properties
/// <summary>
/// Determines if errors should be thrown if any casting errors take place
/// </summary>
public bool SupressExceptions { get; set; }
/// <summary>
/// Accessess a property by name and returns an object
/// </summary>
public object this[string property] {
get {
return this.Get<object>(property);
}
}
#endregion
#region Public Methods
/// <summary>
/// Checks if this Anonymous Type has the specified property
/// </summary>
public bool Has(string property) {
return ((m_Type.GetProperty(property) as PropertyInfo) != null);
}
/// <summary>
/// Returns if this Anonymous type has the specified property and that
/// the value matches the type specified
/// </summary>
public bool Has(string property, Type isType) {
//try and get the property
PropertyInfo prop = m_Type.GetProperty(property) as PropertyInfo;
//If this type doesn't exist at all, just return false
if (prop == null) { return false; }
//if it does exist, verify the type
if (prop.PropertyType.Equals(isType)) { return true; }
return false;
}
/// <summary>
/// Returns a type value using the specified type
/// </summary>
public T Get<T>(string property) {
//return this value if needed
PropertyInfo prop = m_Type.GetProperty(property) as PropertyInfo;
try {
return (T)prop.GetValue(this.m_TypeData, null);
}
catch (Exception ex) {
if (this.SupressExceptions) { return default(T); }
throw new Exception(
string.Format(EXCEPTION_COULD_NOT_ACCESS_FIELD, property, typeof(T).Name),
ex
);
}
}
/// <summary>
/// Returns a type value using the specified type
/// </summary>
public T Get<T>(string property, object[] index) {
//return this value if needed
PropertyInfo prop = m_Type.GetProperty(property) as PropertyInfo;
try {
return (T)prop.GetValue(this.m_TypeData, index);
}
catch (Exception ex) {
if (this.SupressExceptions) { return default(T); }
throw new Exception(
string.Format(EXCEPTION_COULD_NOT_ACCESS_FIELD_AT_INDEX, property, typeof(T).Name),
ex
);
}
}
/// <summary>
/// Returns a type value using the specified type but includes a default value
/// if one it missing
/// </summary>
public T Get<T>(string property, T defaultValue) {
//return this value if needed
PropertyInfo prop = m_Type.GetProperty(property) as PropertyInfo;
if (prop == null) { return defaultValue; }
try {
return (T)prop.GetValue(this.m_TypeData, null);
}
catch (Exception ex) {
if (this.SupressExceptions) { return defaultValue; }
throw new Exception(
string.Format(EXCEPTION_COULD_NOT_ACCESS_FIELD, prop, typeof(T).Name),
ex
);
}
}
/// <summary>
/// Accepts a delegate that will use the names of the passed in
/// parameters as properties to map to. If the property does not
/// exist, then the method will fail.
/// </summary>
public void Use<T1>(Action<T1> with) {
//set a default for each of the params
T1 param1 = default(T1);
//get the parameters for this method
var paramList = with.Method.GetParameters();
//update each of the parameters
string paramName = string.Empty;
try {
for (int i = 0; i < paramList.Length; i++) {
//find the correct matching property for this parameter
paramName = paramList[i].Name;
switch (i + 1) {
case 1:
param1 = this.Get<T1>(paramName);
break;
}
}
}
catch (Exception ex) {
throw new ArgumentException(
string.Format(EXCEPTION_MISSING_PARAMETER_INFORMATION, paramName),
ex
);
}
//otherwise, execute the method provided
with(param1);
}
/// <summary>
/// Accepts a delegate that will use the names of the passed in
/// parameters as properties to map to. If the property does not
/// exist, then the method will fail.
/// </summary>
public void Use<T1, T2>(Action<T1, T2> with) {
//set a default for each of the params
T1 param1 = default(T1);
T2 param2 = default(T2);
//get the parameters for this method
var paramList = with.Method.GetParameters();
//update each of the parameters
string paramName = string.Empty;
try {
for (int i = 0; i < paramList.Length; i++) {
//find the correct matching property for this parameter
paramName = paramList[i].Name;
switch (i + 1) {
case 1:
param1 = this.Get<T1>(paramName);
break;
case 2:
param2 = this.Get<T2>(paramName);
break;
}
}
}
catch (Exception ex) {
throw new ArgumentException(
string.Format(EXCEPTION_MISSING_PARAMETER_INFORMATION, paramName),
ex
);
}
//otherwise, execute the method provided
with(param1, param2);
}
/// <summary>
/// Accepts a delegate that will use the names of the passed in
/// parameters as properties to map to. If the property does not
/// exist, then the method will fail.
/// </summary>
public void Use<T1, T2, T3>(Action<T1, T2, T3> with) {
//set a default for each of the params
T1 param1 = default(T1);
T2 param2 = default(T2);
T3 param3 = default(T3);
//get the parameters for this method
var paramList = with.Method.GetParameters();
//update each of the parameters
string paramName = string.Empty;
try {
for (int i = 0; i < paramList.Length; i++) {
//find the correct matching property for this parameter
paramName = paramList[i].Name;
switch (i + 1) {
case 1:
param1 = this.Get<T1>(paramName);
break;
case 2:
param2 = this.Get<T2>(paramName);
break;
case 3:
param3 = this.Get<T3>(paramName);
break;
}
}
}
catch (Exception ex) {
throw new ArgumentException(
string.Format(EXCEPTION_MISSING_PARAMETER_INFORMATION, paramName),
ex
);
}
//otherwise, execute the method provided
with(param1, param2, param3);
}
/// <summary>
/// Accepts a delegate that will use the names of the passed in
/// parameters as properties to map to. If the property does not
/// exist, then the method will fail.
/// </summary>
public void Use<T1, T2, T3, T4>(Action<T1, T2, T3, T4> with) {
//set a default for each of the params
T1 param1 = default(T1);
T2 param2 = default(T2);
T3 param3 = default(T3);
T4 param4 = default(T4);
//get the parameters for this method
var paramList = with.Method.GetParameters();
//update each of the parameters
string paramName = string.Empty;
try {
for (int i = 0; i < paramList.Length; i++) {
//find the correct matching property for this parameter
paramName = paramList[i].Name;
switch (i + 1) {
case 1:
param1 = this.Get<T1>(paramName);
break;
case 2:
param2 = this.Get<T2>(paramName);
break;
case 3:
param3 = this.Get<T3>(paramName);
break;
case 4:
param4 = this.Get<T4>(paramName);
break;
}
}
}
catch (Exception ex) {
throw new ArgumentException(
string.Format(EXCEPTION_MISSING_PARAMETER_INFORMATION, paramName),
ex
);
}
//otherwise, execute the method provided
with(param1, param2, param3, param4);
}
#endregion
#region Working With Arrays
/// <summary>
/// Returns the specified property as an array of AnonymousTypes
/// </summary>
public AnonymousType[] AsArray(string property) {
object[] values = this.Get<object[]>(property);
return values.Select(o => {
if (o is AnonymousType) { return (AnonymousType)o; }
return new AnonymousType(o);
}).ToArray();
}
/// <summary>
/// Performs the specified action on each value in an array of AnonymousTypes
/// </summary>
public void WithEach(string property, Action<AnonymousType> action) {
foreach (AnonymousType value in this.AsArray(property)) {
action(value);
}
}
#endregion
#region Static Methods
/// <summary>
/// Returns the type of data for the provided object
/// </summary>
public static T Get<T>(object data, string property) {
return new AnonymousType(data).Get<T>(property);
}
/// <summary>
/// Returns the type of data for the provided object
/// </summary>
public static T Get<T>(object data, string property, T defaultValue) {
return new AnonymousType(data).Get<T>(property, defaultValue);
}
/// <summary>
/// Returns the type of data for the provided object
/// </summary>
public static AnonymousType[] AsArray(object data, string property) {
return new AnonymousType(data).AsArray(property);
}
/// <summary>
/// Performs the following action on each of the values in the specified
/// property value for a user
/// </summary>
public static void WithEach(object data, string property, Action<AnonymousType> action) {
new AnonymousType(data).WithEach(property, action);
}
#endregion
}
}
考虑显式转换为列表并转换ViewData：
ViewData["QUsers"] = (from u in db.Users select u).ToList();
foreach(Users u in (List<Users>)ViewData["QUsers"]){
/*Print the data here*/
}
您可以通过几种方式传递数据，使用上面的ViewData或TempData在Actions之间传递。您还可以使用ViewData.Model来包含强类型模型。请注意，您必须将视图的定义更改为
ViewPage<User>
对于一个不错的中继器更换，请尝试 http://www.codeplex.com/MVCContrib 。他们有一个可能有帮助的Grid Html Helper。
如果你想避免创建一个单独的类只是为了显示你的一个投影，你也可以使用字典，如下所示：
from person in personList select new Dictionary<string, string>
{
{ "Name", person.Firstname + " " + person.Lastname },
{ "Id", person.Id.ToString() }
};
然后，您可以将您的视图页面输入
ViewPage<IEnumerable<Dictionary<string, string>>>
最后迭代遍历视图中的列表：
<% foreach (Dictionary<string, string> p in (IEnumerable)ViewData.Model)
{ %>
<li> <%=p["Id"] %> - <%= p["Name"] %> </li>
<% } %>
毋庸置疑，缺点是您的代码现在充满了<！>“魔术字符串<！>”，因为缺少编译时间检查而使其更容易出错。
你不能只使用MVC中的RouteValueDictionary吗？
不隶属于 StackOverflow
