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Orm框架开发之NewExpression合并问题

之前都是看别人写博客,自己没有写博客的习惯.在工作的过程中,总是会碰到许多的技术问题.有很多时候想记录下来,后面一直有许多的问题等着解决.总想着等系统完成了,再回头总结下.往往结果就把这事抛到脑后了.

总觉得不能一直这样哈.今天简单记一下吧.有表达不清楚的地方,多多包涵.

最近在研究.net orm框架.想开发一套更好用的Orm框架.碰到一个Expression合并的问题.别嫌轮子多.

一.需求情况描述

需要更新部分数据的时候,可能前端传回的只有部分字段的数据.而更新的时候,需要设置更新人,更新日期等.

举个栗子来说:

现在有一个预约信息表

前端需要修改数据内容如下,我们暂且叫表达A

var exp = ExpressionHelper.CreateExpression<AppointmentDto>(a => new {
    a.Id,
    a.PatientName,
    a.PatientNamePy,
    a.IdentityCardNumber,
    a.Birthday,
    a.PatientAge,
    a.PatientSex,
    a.PatientPhone,
    a.Address
});

而写入数据库的时候需要添加更新人,更新时间.LastUpdateUserId和UpdateTime.

于是我们便又多了一个lambda表达式,我们叫它表达式B

var exp = ExpressionHelper.CreateExpression<AppointmentDto>(a => new {
    a.Id,
    a.PatientName,
    a.PatientNamePy,
    a.IdentityCardNumber,
    a.Birthday,
    a.PatientAge,
    a.PatientSex,
    a.PatientPhone,
    a.Address,
    a.LastUpdateUserId,
    a.UpdateTime
});

这里说下ExpressionHelper.CreateExpression<T>方法,只是一个为了缩减代码长度而写的方法.输入的lambda表达式原样返回了.

外面不用写好长的类型了.Expression这个类型平时不用.写外面看着眼晕. Expression<Func<AppointmentDto, object>> exp1 = a => new {a.Id,a.PatientName};

/// <summary>
/// 转换Expr
/// 在外面调用时可以使用var以减少代码长度
/// </summary>
/// <param name="expr"></param>
/// <returns></returns>
public static Expression<Func<T, object>> CreateExpression<T>(Expression<Func<T, object>> expr)
{
    return expr;
}

所以此处,使用var可以看起来更整洁.但并不推荐在正常情况下使用var.

个人觉得使用var让代码可维护性降低.读起来真的是头疼.之前在维护一个比较大的系统的时候,公司的主要项目,缺少项目文档,代码里面也基本上没啥注释.而且又清一色的var,每个方法返回的是啥类型?你得去方法那边看去.看着真是恼火,又不得不去一点一点的改.都改成相应的类型后,看着就清爽多了.看一眼,流程就基本上能明白大概.所以,var在C#这种强类型语言里,能不用就别用了.

上面就当是发牢骚了.我们回到正题.

我们看到表达式B比表达式A只多了两个字段.大多数代码都是重复的.而且,两个lambda表达式严重的加长了代码行数.几个这样的表达式下来,这个类就到了几百行了.

对于喜欢简洁,简单的我来说,类一大了我就头疼.那咋整?要是有办法将这两个表达式简化处理一下就好了.将表达式A加上一个短的表达式,来实现表达式B呢.

比如实现 var exprB = exprA.Add(a => new { a.PatientPhone });

So,开始捯饬...

二.解决方法

因为这个合并表达式的方法是在个人系统内部使用满足我定制的Orm的类名称需求

所以定义了一个新的Expression表达式类型NewObjectExpression来处理

  1     /// <summary>
  2     /// New Object Expression
  3     /// 合并NewExpression使用.
  4     /// </summary>
  5     public class NewObjectExpression : Expression, IArgumentProvider
  6     {
  7         private IList<Expression> arguments;
  8 
  9         /// <summary>
 10         /// 构造方法
 11         /// </summary>
 12         /// <param name="constructor"></param>
 13         /// <param name="arguments"></param>
 14         /// <param name="members"></param>
 15         internal NewObjectExpression(ConstructorInfo constructor, IList<Expression> arguments, List<MemberInfo> members)
 16         {
 17             this.Constructor = constructor;
 18             this.arguments = arguments;
 19             this.Members = members;
 20 
 21             if (members != null)
 22             {
 23                 List<string> nameList = members.Select(member => member.Name).ToList();
 24                 for (int i = 0; i < nameList.Count; i++)
 25                 {
 26                     if (!string.IsNullOrEmpty(ExpressionString))
 27                     {
 28                         ExpressionString += "," + nameList[i];
 29                     }
 30                     else
 31                     {
 32                         ExpressionString = nameList[i];
 33                     }
 34                 }
 35             }
 36         }
 37 
 38         /// <summary>
 39         /// Gets the static type of the expression that this <see cref="Expression" /> represents. (Inherited from <see cref="Expression"/>.)
 40         /// </summary>
 41         /// <returns>The <see cref="Type"/> that represents the static type of the expression.</returns>
 42         public override Type Type
 43         {
 44             get { return Constructor.DeclaringType; }
 45         }
 46 
 47         /// <summary>
 48         /// Returns the node type of this <see cref="Expression" />. (Inherited from <see cref="Expression" />.)
 49         /// </summary>
 50         /// <returns>The <see cref="ExpressionType"/> that represents this expression.</returns>
 51         public sealed override ExpressionType NodeType
 52         {
 53             get { return ExpressionType.New; }
 54         }
 55 
 56         /// <summary>
 57         /// Gets the called constructor.
 58         /// </summary>
 59         public ConstructorInfo Constructor { get; }
 60 
 61         /// <summary>
 62         /// Gets the arguments to the constructor.
 63         /// </summary>
 64         public ReadOnlyCollection<Expression> Arguments
 65         {
 66             get { return (ReadOnlyCollection<Expression>)arguments; }
 67         }
 68 
 69         Expression IArgumentProvider.GetArgument(int index)
 70         {
 71             return arguments[index];
 72         }
 73 
 74         int IArgumentProvider.ArgumentCount
 75         {
 76             get
 77             {
 78                 return arguments.Count;
 79             }
 80         }
 81         
 82         /// <summary>
 83         /// ExpressionString
 84         /// </summary>
 85         public string ExpressionString { get; private set; } = "";
 86 
 87         public ConstructorInfo Constructor1 => Constructor;
 88 
 89         public List<MemberInfo> Members { get; set; }
 90 
 91         /// <summary>
 92         /// 更新members
 93         /// </summary>
 94         /// <param name="arguments"></param>
 95         /// <param name="members"></param>
 96         /// <returns></returns>
 97         public NewObjectExpression Update(IList<Expression> arguments, List<MemberInfo> members)
 98         {
 99             if (arguments != null)
100             {
101                 this.arguments = arguments;
102             }
103             if (Members != null)
104             {
105                 this.Members = members;
106                 ExpressionString = "";
107                 List<string> nameList = members.Select(member => member.Name).ToList();
108                 for (int i = 0; i < nameList.Count; i++)
109                 {
110                     if (!string.IsNullOrEmpty(ExpressionString))
111                     {
112                         ExpressionString += "," + nameList[i];
113                     }
114                     else
115                     {
116                         ExpressionString = nameList[i];
117                     }
118                 }                
119             }
120             return this;
121         }
122     }

View Code

待处理的属性都放到了Members里面.后面解析使用的也是Members.其它方法Copy自NewExpression的源码,可以删了不用.

下面我们来扩展Expression<Func<T, object>>,让Expression<Func<T, object>>拥有Add和Remove属性的方法.

直接上代码,看前两个方法.后面两个方法是扩展Expression<Func<T, bool>>表达式的And和Or.等有回头有空再介绍.

  1     /// <summary>
  2     /// Expression 扩展
  3     /// </summary>
  4     public static class ExpressionExpand
  5     {
  6         /// <summary>
  7         /// Expression And 
  8         /// NewExpression 合并
  9         /// </summary>
 10         /// <param name="expr"></param>
 11         /// <returns></returns>
 12         public static Expression<Func<T, object>> Add<T>(this Expression<Func<T, object>> expr, Expression<Func<T, object>> expandExpr)
 13         {
 14             Expression<Func<T, object>> result = null;
 15             ParameterExpression parameter = Expression.Parameter(typeof(T), "p");
 16             List<MemberInfo> memberInfoList = new List<MemberInfo>();
 17             #region 处理原expr
 18             if (expr.Body is NewExpression)
 19             {   // t=>new{t.Id,t.Name}
 20                 NewExpression newExp = expr.Body as NewExpression;
 21                 if (newExp.Members != null)
 22                 {
 23                     memberInfoList = newExp.Members.ToList();
 24                 }
 25             }
 26             else if (expr.Body is NewObjectExpression)
 27             {
 28                 NewObjectExpression newExp = expr.Body as NewObjectExpression;
 29                 if (newExp.Members != null)
 30                 {
 31                     memberInfoList = newExp.Members.ToList();
 32                 }
 33             }
 34             else if (expr.Body is UnaryExpression)
 35             {   //t=>t.Id
 36                 UnaryExpression unaryExpression = expr.Body as UnaryExpression;
 37                 MemberExpression memberExp = unaryExpression.Operand as MemberExpression;
 38                 memberInfoList.Add(memberExp.Member);
 39             }
 40             #endregion
 41 
 42             #region 处理扩展expr
 43             if (expandExpr.Body is NewExpression)
 44             {   // t=>new{t.Id,t.Name}
 45                 NewExpression newExp = expandExpr.Body as NewExpression;
 46                 for (int i = 0; i < newExp.Members.Count; i++)
 47                 {
 48                     MemberExpression memberExp = Expression.Property(parameter, newExp.Members[i].Name);
 49                     if (!memberInfoList.Any(member => member.Name == newExp.Members[i].Name))
 50                     {
 51                         memberInfoList.Add(newExp.Members[i]);
 52                     }
 53                 }
 54             }
 55             else if (expr.Body is NewObjectExpression)
 56             {
 57                 NewObjectExpression newExp = expr.Body as NewObjectExpression;
 58                 if (newExp.Members != null && newExp.Members.Count > 0)
 59                 {
 60                     for (int i = 0; i < newExp.Members.Count; i++)
 61                     {
 62                         MemberExpression memberExp = Expression.Property(parameter, newExp.Members[i].Name);
 63                         if (!memberInfoList.Any(member => member.Name == newExp.Members[i].Name))
 64                         {
 65                             memberInfoList.Add(newExp.Members[i]);
 66                         }
 67                     }
 68                 }
 69             }
 70             else if (expandExpr.Body is UnaryExpression)
 71             {   //t=>t.Id
 72                 UnaryExpression unaryExpression = expandExpr.Body as UnaryExpression;
 73                 MemberExpression memberExp = unaryExpression.Operand as MemberExpression;
 74                 if (!memberInfoList.Any(exp => exp.Name == memberExp.Member.Name))
 75                 {
 76                     memberInfoList.Add(memberExp.Member);
 77                 }
 78             }
 79             #endregion
 80             NewObjectExpression newObjExpression = new NewObjectExpression(typeof(object).GetConstructors()[0], null, memberInfoList);
 81             result = Expression.Lambda<Func<T, object>>(newObjExpression, parameter);
 82             return result;
 83         }
 84 
 85         /// <summary>
 86         /// Expression Remove 
 87         /// NewExpression 合并
 88         /// </summary>
 89         /// <param name="expr"></param>
 90         /// <returns></returns>
 91         public static Expression<Func<T, object>> Remove<T>(this Expression<Func<T, object>> expr, Expression<Func<T, object>> expandExpr)
 92         {
 93             Expression<Func<T, object>> result = null;
 94             ParameterExpression parameter = Expression.Parameter(typeof(T), "p");
 95             List<MemberInfo> memberInfoList = new List<MemberInfo>();
 96             List<MemberInfo> removeMemberInfoList = new List<MemberInfo>();
 97             #region 处理原expr
 98             if (expr.Body is NewExpression)
 99             {   // t=>new{t.Id,t.Name}
100                 NewExpression newExp = expr.Body as NewExpression;
101                 if (newExp.Members != null)
102                 {
103                     memberInfoList = newExp.Members.ToList();
104                 }
105             }
106             else if (expr.Body is NewObjectExpression)
107             {
108                 NewObjectExpression newExp = expr.Body as NewObjectExpression;
109                 if (newExp.Members != null)
110                 {
111                     memberInfoList = newExp.Members.ToList();
112                 }
113             }
114             else if (expr.Body is UnaryExpression)
115             {   //t=>t.Id
116                 UnaryExpression unaryExpression = expr.Body as UnaryExpression;
117                 MemberExpression memberExp = unaryExpression.Operand as MemberExpression;
118                 memberInfoList.Add(memberExp.Member);
119             }
120             #endregion
121 
122             #region 处理扩展expr
123             if (expandExpr.Body is NewExpression)
124             {   // t=>new{t.Id,t.Name}
125                 NewExpression newExp = expandExpr.Body as NewExpression;
126                 for (int i = 0; i < newExp.Members.Count; i++)
127                 {
128                     MemberExpression memberExp = Expression.Property(parameter, newExp.Members[i].Name);
129                     if (!removeMemberInfoList.Any(member => member.Name == newExp.Members[i].Name))
130                     {
131                         removeMemberInfoList.Add(newExp.Members[i]);
132                     }
133                 }
134             }
135             else if (expr.Body is NewObjectExpression)
136             {
137                 NewObjectExpression newExp = expr.Body as NewObjectExpression;
138                 if (newExp.Members != null && newExp.Members.Count > 0)
139                 {
140                     for (int i = 0; i < newExp.Members.Count; i++)
141                     {
142                         MemberExpression memberExp = Expression.Property(parameter, newExp.Members[i].Name);
143                         if (!removeMemberInfoList.Any(member => member.Name == newExp.Members[i].Name))
144                         {
145                             removeMemberInfoList.Add(newExp.Members[i]);
146                         }
147                     }
148                 }
149             }
150             else if (expandExpr.Body is UnaryExpression)
151             {   //t=>t.Id
152                 UnaryExpression unaryExpression = expandExpr.Body as UnaryExpression;
153                 MemberExpression memberExp = unaryExpression.Operand as MemberExpression;
154                 if (!memberInfoList.Any(exp => exp.Name == memberExp.Member.Name))
155                 {
156                     removeMemberInfoList.Add(memberExp.Member);
157                 }
158             }
159             #endregion
160 
161             for (int i = memberInfoList.Count - 1; i >= 0; i--)
162             {
163                 if (removeMemberInfoList.Any(member => member.Name == memberInfoList[i].Name))
164                 {
165                     memberInfoList.Remove(memberInfoList[i]);
166                 }
167             }
168             if (memberInfoList.Count <= 0)
169             {
170                 throw new System.Exception("Expression Remove Error.All Properties are removed.");
171             }
172             NewObjectExpression newObjExpression = new NewObjectExpression(typeof(object).GetConstructors()[0], null, memberInfoList);
173             result = Expression.Lambda<Func<T, object>>(newObjExpression, parameter);
174             return result;
175         }
176 
177         /// <summary>
178         /// Expression And
179         /// </summary>
180         /// <param name="expr"></param>
181         /// <returns></returns>
182         public static Expression<Func<T, bool>> And<T>(this Expression<Func<T, bool>> expr, Expression<Func<T, bool>> expandExpr)
183         {
184             Expression<Func<T, bool>> result = Expression.Lambda<Func<T, bool>>(Expression.And(expandExpr.Body, expr.Body), expr.Parameters);
185             return result;
186         }
187 
188         /// <summary>
189         /// Expression And
190         /// </summary>
191         /// <param name="expr"></param>
192         /// <returns></returns>
193         public static Expression<Func<T, bool>> Or<T>(this Expression<Func<T, bool>> expr, Expression<Func<T, bool>> expandExpr)
194         {
195             Expression<Func<T, bool>> result = Expression.Lambda<Func<T, bool>>(Expression.Or(expandExpr.Body, expr.Body), expr.Parameters);
196             return result;
197         }
198     }

View Code

Add方法可处理 NewExpression 类似 t=>new{t.Id,t.Name} , UnaryExpression 类似t=>t.Id,以及我们自定义的NewObjectExpression类型

所以我们在更新数据的时候就可以这么写了:

Dbc.Db.Update(dto, exp.Add(a => a.LastUpdateUserId));
Dbc.Db.Update(dto, exp.Add(a => new { a.LastUpdateUserId, a.UpdateTime }));

在Orm框架内部,解析NewObjectExpression时,解析方法如下

 1         /// <summary>
 2         /// 通过Lambed Expression获取属性名称
 3         /// </summary>
 4         /// <param name="expr">查询表达式</param>
 5         /// <returns></returns>
 6         public static List<string> GetPiList<T>(Expression<Func<T, object>> expr)
 7         {
 8             List<string> result = new List<string>();
 9             if (expr.Body is NewExpression)
10             {   // t=>new{t.Id,t.Name}
11                 NewExpression nexp = expr.Body as NewExpression;
12                 if (nexp.Members != null)
13                 {
14                     result = nexp.Members.Select(member => member.Name).ToList();
15                 }
16             }
17             else if (expr.Body is NewObjectExpression)
18             {   // t=>new{t.Id,t.Name}
19                 NewObjectExpression nexp = expr.Body as NewObjectExpression;
20                 if (nexp.Members != null)
21                 {
22                     result = nexp.Members.Select(member => member.Name).ToList();
23                 }
24             }
25             else if (expr.Body is UnaryExpression)
26             {   //t=>t.Id
27                 UnaryExpression uexp = expr.Body as UnaryExpression;
28                 MemberExpression mexp = uexp.Operand as MemberExpression;
29                 result.Add(mexp.Member.Name);
30             }
31             else
32             {
33                 throw new System.Exception("不支持的Select lambda写法");
34             }
35             return result;
36         }

View Code

至此,就完成了Expression<Func<T, object>>Add和Remove属性的扩展,Orm可以让代码更简洁.

三.后记

其实在使用新的类NewObjectExpression来解决之前,尝试过其它的许多方式,因为使用.net的类型可以在其它的框架程序中借鉴引用.不必局限在个人框架内部.

NewExpression内部有一些校验,本身Expression<Func<T, object>>是一个匿名类.试过处理NewExpression,以及新建类继承自NewExpression等方式.都没成功.

要是大家有更好的方法欢迎留言告知.希望本文能对大家有所帮助.

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原文地址：https://www.cnblogs.com/arthur3k/p/10244293.html