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

     /// <summary>
     /// New Object Expression
     /// 合并NewExpression使用.
     /// </summary>
     public class NewObjectExpression : Expression, IArgumentProvider
     {
         private IList<Expression> arguments;

         /// <summary>
         /// 构造方法
         /// </summary>
         /// <param name="constructor"></param>
         /// <param name="arguments"></param>
         /// <param name="members"></param>
         internal NewObjectExpression(ConstructorInfo constructor, IList<Expression> arguments, List<MemberInfo> members)
         {
             this.Constructor = constructor;
             this.arguments = arguments;
             this.Members = members;

             if (members != null)
             {
                 List<string> nameList = members.Select(member => member.Name).ToList();
                 for (int i = ; i < nameList.Count; i++)
                 {
                     if (!string.IsNullOrEmpty(ExpressionString))
                     {
                         ExpressionString += "," + nameList[i];
                     }
                     else
                     {
                         ExpressionString = nameList[i];
                     }
                 }
             }
         }

         /// <summary>
         /// Gets the static type of the expression that this <see cref="Expression" /> represents. (Inherited from <see cref="Expression"/>.)
         /// </summary>
         /// <returns>The <see cref="Type"/> that represents the static type of the expression.</returns>
         public override Type Type
         {
             get { return Constructor.DeclaringType; }
         }

         /// <summary>
         /// Returns the node type of this <see cref="Expression" />. (Inherited from <see cref="Expression" />.)
         /// </summary>
         /// <returns>The <see cref="ExpressionType"/> that represents this expression.</returns>
         public sealed override ExpressionType NodeType
         {
             get { return ExpressionType.New; }
         }

         /// <summary>
         /// Gets the called constructor.
         /// </summary>
         public ConstructorInfo Constructor { get; }

         /// <summary>
         /// Gets the arguments to the constructor.
         /// </summary>
         public ReadOnlyCollection<Expression> Arguments
         {
             get { return (ReadOnlyCollection<Expression>)arguments; }
         }

         Expression IArgumentProvider.GetArgument(int index)
         {
             return arguments[index];
         }

         int IArgumentProvider.ArgumentCount
         {
             get
             {
                 return arguments.Count;
             }
         }

         /// <summary>
         /// ExpressionString
         /// </summary>
         public string ExpressionString { get; private set; } = "";

         public ConstructorInfo Constructor1 => Constructor;

         public List<MemberInfo> Members { get; set; }

         /// <summary>
         /// 更新members
         /// </summary>
         /// <param name="arguments"></param>
         /// <param name="members"></param>
         /// <returns></returns>
         public NewObjectExpression Update(IList<Expression> arguments, List<MemberInfo> members)
         {
             if (arguments != null)
             {
                 this.arguments = arguments;
             }
             if (Members != null)
             {
                 this.Members = members;
                 ExpressionString = "";
                 List<string> nameList = members.Select(member => member.Name).ToList();
                 for (int i = ; i < nameList.Count; i++)
                 {
                     if (!string.IsNullOrEmpty(ExpressionString))
                     {
                         ExpressionString += "," + nameList[i];
                     }
                     else
                     {
                         ExpressionString = nameList[i];
                     }
                 }
             }
             return this;
         }
     }

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.

     /// <summary>
     /// Expression 扩展
     /// </summary>
     public static class ExpressionExpand
     {
         /// <summary>
         /// Expression And
         /// NewExpression 合并
         /// </summary>
         /// <param name="expr"></param>
         /// <returns></returns>
         public static Expression<Func<T, object>> Add<T>(this Expression<Func<T, object>> expr, Expression<Func<T, object>> expandExpr)
         {
             Expression<Func<T, object>> result = null;
             ParameterExpression parameter = Expression.Parameter(typeof(T), "p");
             List<MemberInfo> memberInfoList = new List<MemberInfo>();
             #region 处理原expr
             if (expr.Body is NewExpression)
             {   // t=>new{t.Id,t.Name}
                 NewExpression newExp = expr.Body as NewExpression;
                 if (newExp.Members != null)
                 {
                     memberInfoList = newExp.Members.ToList();
                 }
             }
             else if (expr.Body is NewObjectExpression)
             {
                 NewObjectExpression newExp = expr.Body as NewObjectExpression;
                 if (newExp.Members != null)
                 {
                     memberInfoList = newExp.Members.ToList();
                 }
             }
             else if (expr.Body is UnaryExpression)
             {   //t=>t.Id
                 UnaryExpression unaryExpression = expr.Body as UnaryExpression;
                 MemberExpression memberExp = unaryExpression.Operand as MemberExpression;
                 memberInfoList.Add(memberExp.Member);
             }
             #endregion

             #region 处理扩展expr
             if (expandExpr.Body is NewExpression)
             {   // t=>new{t.Id,t.Name}
                 NewExpression newExp = expandExpr.Body as NewExpression;
                 for (int i = ; i < newExp.Members.Count; i++)
                 {
                     MemberExpression memberExp = Expression.Property(parameter, newExp.Members[i].Name);
                     if (!memberInfoList.Any(member => member.Name == newExp.Members[i].Name))
                     {
                         memberInfoList.Add(newExp.Members[i]);
                     }
                 }
             }
             else if (expr.Body is NewObjectExpression)
             {
                 NewObjectExpression newExp = expr.Body as NewObjectExpression;
                 if (newExp.Members != null && newExp.Members.Count > )
                 {
                     for (int i = ; i < newExp.Members.Count; i++)
                     {
                         MemberExpression memberExp = Expression.Property(parameter, newExp.Members[i].Name);
                         if (!memberInfoList.Any(member => member.Name == newExp.Members[i].Name))
                         {
                             memberInfoList.Add(newExp.Members[i]);
                         }
                     }
                 }
             }
             else if (expandExpr.Body is UnaryExpression)
             {   //t=>t.Id
                 UnaryExpression unaryExpression = expandExpr.Body as UnaryExpression;
                 MemberExpression memberExp = unaryExpression.Operand as MemberExpression;
                 if (!memberInfoList.Any(exp => exp.Name == memberExp.Member.Name))
                 {
                     memberInfoList.Add(memberExp.Member);
                 }
             }
             #endregion
             NewObjectExpression newObjExpression = new NewObjectExpression(typeof(object).GetConstructors()[], null, memberInfoList);
             result = Expression.Lambda<Func<T, object>>(newObjExpression, parameter);
             return result;
         }

         /// <summary>
         /// Expression Remove
         /// NewExpression 合并
         /// </summary>
         /// <param name="expr"></param>
         /// <returns></returns>
         public static Expression<Func<T, object>> Remove<T>(this Expression<Func<T, object>> expr, Expression<Func<T, object>> expandExpr)
         {
             Expression<Func<T, object>> result = null;
             ParameterExpression parameter = Expression.Parameter(typeof(T), "p");
             List<MemberInfo> memberInfoList = new List<MemberInfo>();
             List<MemberInfo> removeMemberInfoList = new List<MemberInfo>();
             #region 处理原expr
             if (expr.Body is NewExpression)
             {   // t=>new{t.Id,t.Name}
                 NewExpression newExp = expr.Body as NewExpression;
                 if (newExp.Members != null)
                 {
                     memberInfoList = newExp.Members.ToList();
                 }
             }
             else if (expr.Body is NewObjectExpression)
             {
                 NewObjectExpression newExp = expr.Body as NewObjectExpression;
                 if (newExp.Members != null)
                 {
                     memberInfoList = newExp.Members.ToList();
                 }
             }
             else if (expr.Body is UnaryExpression)
             {   //t=>t.Id
                 UnaryExpression unaryExpression = expr.Body as UnaryExpression;
                 MemberExpression memberExp = unaryExpression.Operand as MemberExpression;
                 memberInfoList.Add(memberExp.Member);
             }
             #endregion

             #region 处理扩展expr
             if (expandExpr.Body is NewExpression)
             {   // t=>new{t.Id,t.Name}
                 NewExpression newExp = expandExpr.Body as NewExpression;
                 for (int i = ; i < newExp.Members.Count; i++)
                 {
                     MemberExpression memberExp = Expression.Property(parameter, newExp.Members[i].Name);
                     if (!removeMemberInfoList.Any(member => member.Name == newExp.Members[i].Name))
                     {
                         removeMemberInfoList.Add(newExp.Members[i]);
                     }
                 }
             }
             else if (expr.Body is NewObjectExpression)
             {
                 NewObjectExpression newExp = expr.Body as NewObjectExpression;
                 if (newExp.Members != null && newExp.Members.Count > )
                 {
                     for (int i = ; i < newExp.Members.Count; i++)
                     {
                         MemberExpression memberExp = Expression.Property(parameter, newExp.Members[i].Name);
                         if (!removeMemberInfoList.Any(member => member.Name == newExp.Members[i].Name))
                         {
                             removeMemberInfoList.Add(newExp.Members[i]);
                         }
                     }
                 }
             }
             else if (expandExpr.Body is UnaryExpression)
             {   //t=>t.Id
                 UnaryExpression unaryExpression = expandExpr.Body as UnaryExpression;
                 MemberExpression memberExp = unaryExpression.Operand as MemberExpression;
                 if (!memberInfoList.Any(exp => exp.Name == memberExp.Member.Name))
                 {
                     removeMemberInfoList.Add(memberExp.Member);
                 }
             }
             #endregion

             for (int i = memberInfoList.Count - ; i >= ; i--)
             {
                 if (removeMemberInfoList.Any(member => member.Name == memberInfoList[i].Name))
                 {
                     memberInfoList.Remove(memberInfoList[i]);
                 }
             }
             if (memberInfoList.Count <= )
             {
                 throw new System.Exception("Expression Remove Error.All Properties are removed.");
             }
             NewObjectExpression newObjExpression = new NewObjectExpression(typeof(object).GetConstructors()[], null, memberInfoList);
             result = Expression.Lambda<Func<T, object>>(newObjExpression, parameter);
             return result;
         }

         /// <summary>
         /// Expression And
         /// </summary>
         /// <param name="expr"></param>
         /// <returns></returns>
         public static Expression<Func<T, bool>> And<T>(this Expression<Func<T, bool>> expr, Expression<Func<T, bool>> expandExpr)
         {
             Expression<Func<T, bool>> result = Expression.Lambda<Func<T, bool>>(Expression.And(expandExpr.Body, expr.Body), expr.Parameters);
             return result;
         }

         /// <summary>
         /// Expression And
         /// </summary>
         /// <param name="expr"></param>
         /// <returns></returns>
         public static Expression<Func<T, bool>> Or<T>(this Expression<Func<T, bool>> expr, Expression<Func<T, bool>> expandExpr)
         {
             Expression<Func<T, bool>> result = Expression.Lambda<Func<T, bool>>(Expression.Or(expandExpr.Body, expr.Body), expr.Parameters);
             return result;
         }
     }

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

         /// <summary>
         /// 通过Lambed Expression获取属性名称
         /// </summary>
         /// <param name="expr">查询表达式</param>
         /// <returns></returns>
         public static List<string> GetPiList<T>(Expression<Func<T, object>> expr)
         {
             List<string> result = new List<string>();
             if (expr.Body is NewExpression)
             {   // t=>new{t.Id,t.Name}
                 NewExpression nexp = expr.Body as NewExpression;
                 if (nexp.Members != null)
                 {
                     result = nexp.Members.Select(member => member.Name).ToList();
                 }
             }
             else if (expr.Body is NewObjectExpression)
             {   // t=>new{t.Id,t.Name}
                 NewObjectExpression nexp = expr.Body as NewObjectExpression;
                 if (nexp.Members != null)
                 {
                     result = nexp.Members.Select(member => member.Name).ToList();
                 }
             }
             else if (expr.Body is UnaryExpression)
             {   //t=>t.Id
                 UnaryExpression uexp = expr.Body as UnaryExpression;
                 MemberExpression mexp = uexp.Operand as MemberExpression;
                 result.Add(mexp.Member.Name);
             }
             else
             {
                 throw new System.Exception("不支持的Select lambda写法");
             }
             return result;
         }

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.