本系列目录:
使用EF构建企业级应用(一):主要讲数据库访问基类IRepository及Repository 的实现
使用EF构建企业级应用(二):主要讲动态排序扩展的实现
使用EF构建企业级应用(三):主要讲灵活的构建查询条件表达式Expression<Func<TEntity,bool>>.
使用EF构建企业级应用(四):主要讲下在MVC环境中前端开发中如何邮箱的使用,及一个实例源码包
在前两篇文章中,我们已经实现了基于EF的数据库基本操作基类的构建,以及简单的介绍了如何方便的动态构建排序表达式,在第二篇文章结尾,我们遗漏下来了一个问题:如何方便的构建查询参数(即类似于这样的Expression<TEntity, bool> expression查询表达式)
在往常的经验中,我们知道在和数据库交互的过程中,查询可能是最复杂的,做过数据持久化封装的同学们可能对这个认识尤为突出,其他原因我们就不细说了, 如何丰富的,易用的构建查询条件这个就有点让人迷惑.
我们来分析一个常见的查询条件(a>4 and b<3)Or(d>5 and c in(3,4,5)),
- 设定:var exp1=a>4 and b<3; var exp2=d>5 and c in(3,4,5),则上述条件可以表示为 var exp=exp1 or exp2;
- 进一步分解exp1:var exp1_1=a>4; var exp1_2=b<3; 则exp1=exp1_1 and var exp_2
- 进一步分解exp2:var exp2_1=d>5; var exp2_2=c in (3,4,5); 则exp2=exp2_1 and exp2_2
有了上面的分解,我们发现其实构建这个查询条件非常符合我们常见的递归算法.下面我们尝试一下用递归的思想来实现这个.我们先大致的画个UML草图
为了不和系统下面的Expression 命名混淆,我们这里采用EFExpression作为条件表达式基类名称,
- EFExpression<T> 为一个抽象基类,里面主要有一个返回类型为 Expression<Func<T,bool>> GetExpression()的一个抽象方法,其具体实现,我们放在了每一个具体的Expression中去定义.
- EmptyEFExpression<T> 表示一个空的查询表达式
- BinaryEFExpression<T> 表示一个基于二元条件的查询表达式,如大于,小于,等于 ……
- LikeEFExpression<T> 表示一个用于创建”类似于”条件的查询表达式
- LogicEFExpression<T> 表示一个逻辑运算的查询表达式,如and or
- ….可能还会有其他子类
1.首先我们试着来编写一下抽象基类EFExpression<T>的实现
/// <summary> /// 查询表达式基类 /// </summary> public abstract class EFExpression<T> where T : class { /// <summary> /// 获取查询表达式 /// </summary> /// <returns></returns> public virtual Expression<Func<T, bool>> GetExpression() { if (Expression != null) { var candidateExp = Expression.Parameter(typeof(T), "x"); var exp = Expression.Lambda<Func<T, bool>>(Expression, candidateExp); return exp; } else { return null; } } /// <summary> /// 查询条件对应表达式 /// </summary> protected Expression _Expression { get; set; } /// <summary> /// 参数表达式 /// </summary> public ParameterExpression[] Parameters { get; set; } /// <summary> /// 获取对应的表达式 /// </summary> internal abstract Expression Expression { get; } /// <summary> /// 获取表达式主题 /// </summary> /// <typeparam name="T"></typeparam> /// <typeparam name="P"></typeparam> /// <param name="old"></param> /// <param name="property"></param> /// <returns></returns> protected static Expression GetMemberExpression<T, P>(EFExpression<T> old, Expression<Func<T, P>> property) where T : class { if (old.Parameters == null || old.Parameters.Length == 0) { old.Parameters = property.Parameters.ToArray(); return property.Body; } ParameterExpressionVisitor visitor = new ParameterExpressionVisitor(old.Parameters[0]); Expression memberExpr = visitor.ChangeParameter(property.Body); return memberExpr; } /// <summary> /// 获取一个空的表达式 /// </summary> /// <returns></returns> public Expression<Func<T, bool>> GetEmptyExpression() { return (Expression<Func<T, bool>>)(f => true); } /// <summary> /// 两个条件进行And运算 /// </summary> /// <param name="left"></param> /// <param name="right"></param> /// <returns></returns> public static EFExpression<T> operator &(EFExpression<T> left, EFExpression<T> right) { return new LogicEFExpression<T>(left, ELogicType.And, right); } /// <summary> /// 两个条件进行Or运行 /// </summary> /// <param name="left"></param> /// <param name="right"></param> /// <returns></returns> public static EFExpression<T> operator |(EFExpression<T> left, EFExpression<T> right) { return new LogicEFExpression<T>(left, ELogicType.Or, right); } }
2. 接着我们来看一下如何实现这个BinaryEFExpression<T>
/// <summary> /// 二元运算查询条件 /// </summary> /// <typeparam name="T">查询条件实体类型</typeparam> /// <typeparam name="TVal">需要比较的属性类型</typeparam> internal class BinanryEFExpression<T, TVal> : EFExpression<T> where T : class where TVal : IComparable { /// <summary> /// 定义条件的实体属性 /// </summary> private Expression<Func<T, TVal>> property; /// <summary> /// 比较的值 /// </summary> private TVal val; /// <summary> /// 二元运算符 /// </summary> private EBinaryType binaryType; /// <summary> /// 实例化新的二元查询表达式 /// </summary> /// <param name="property">定义条件的实体属性</param> /// <param name="binaryType">二元运算符</param> /// <param name="val">比较的值</param> public BinanryEFExpression(Expression<Func<T, TVal>> property, EBinaryType binaryType, TVal val) { if (property == null) throw new ArgumentNullException("property"); //if (val == null && binaryType != EBinaryType.Like) // throw new ArgumentNullException("val"); this.property = property; this.val = val; this.binaryType = binaryType; } internal override Expression Expression { get { if (_Expression == null) { var propertyBody = GetMemberExpression(this, property); Type type = typeof(TVal); Expression compareVal = Expression.Constant(val); //如果是Nullable类型，则把value转化成Nullable类型 if (type.IsNullableType()) { compareVal = Expression.Convert(compareVal, type); } Expression tempExp = null; switch (binaryType) { case EBinaryType.Equal: tempExp = Expression.Equal(propertyBody, compareVal); break; case EBinaryType.GreaterThan: tempExp = Expression.GreaterThan(propertyBody, compareVal); break; case EBinaryType.GreaterThanOrEqual: tempExp = Expression.GreaterThanOrEqual(propertyBody, compareVal); break; case EBinaryType.LessThan: tempExp = Expression.LessThan(propertyBody, compareVal); break; case EBinaryType.LessThanOrEqual: tempExp = Expression.LessThanOrEqual(propertyBody, compareVal); break; case EBinaryType.NotEqual: tempExp = Expression.NotEqual(propertyBody, compareVal); break; default: break; } _Expression = tempExp; } return _Expression; } } }
3.我们在来看一下关于表达式逻辑运算的LogicEFExpression<T> 类又是如何实现的
/// <summary>
/// 带有逻辑运算的查询表达式
/// </summary>
/// <typeparam name="T"></typeparam>
public class LogicEFExpression<T> : EFExpression<T> where T : class
{
private EFExpression<T> left;
private EFExpression<T> right;
private ELogicType logicType;
/// <summary>
/// 实例化新的逻辑运算查询表达式
/// </summary>
/// <param name="left"></param>
/// <param name="logicType">逻辑运算类型</param>
/// <param name="right"></param>
public LogicEFExpression(EFExpression<T> left, ELogicType logicType, EFExpression<T> right)
{
if (left == null || right == null)
throw new ArgumentNullException("left 和 right 不能同时为空");
this.left = left;
this.right = right;
this.logicType = logicType;
}
public override Expression<Func<T, bool>> GetExpression()
{
if (left == null)
return right.GetExpression();
else if (right == null)
return left.GetExpression();
else
{
//判断进行运算的两个条件是否为空
if (left is EmptyEFExpression<T> && right is EmptyEFExpression<T>)
return left.GetExpression();
else if (left is EmptyEFExpression<T>)
return right.GetExpression();
else if (right is EmptyEFExpression<T>)
return left.GetExpression();
var leftExp = left.GetExpression();
var rightExp = right.GetExpression();
Expression<Func<T, bool>> exp = null;
if (leftExp == null && rightExp == null)
return new EmptyEFExpression<T>().GetExpression();
else
{
if (leftExp == null)
return rightExp;
else if (rightExp == null)
return leftExp;
else
{
switch (logicType)
{
case ELogicType.And:
exp = leftExp.And(rightExp);
break;
case ELogicType.Or:
exp = leftExp.Or(rightExp);
break;
default:
break;
}
}
}
return exp;
}
}
internal override Expression Expression
{
get
{
return null;
}
}
}
4.为了使用方便,我们在基类中再添加个静态方法
/// <summary>
/// 构建一个二元查询表达式
/// </summary>
/// <typeparam name="TVal">比较值的类型</typeparam>
/// <param name="property">定义条件的实体属性</param>
/// <param name="binaryType">运算符类型</param>
/// <param name="val">比较的值</param>
/// <returns></returns>
public static EFExpression<T> CreateBinaryExpression<TVal>(Expression<Func<T, TVal>> property,
EBinaryType binaryType, TVal val) where TVal : IComparable
{
return new BinanryEFExpression<T, TVal>(property, binaryType, val);
}
5.有了上面的实现,我们来测试下我们的想法.为了让我们更容易理解,我们假设在一个订单管理环境中,有如下一个需求:请查询满足以下任意一个条件中的订单记录
- 订单状态还未送货且金额>50W的
- 订单状态为送货中,且客户地址在深圳片区的
为了便于理解,我们在这里先定义两个实体类
/// <summary>
/// 订单主表
/// </summary>
public class OrderMain
{
public Guid Id { get; set; }
public string Code { get; set; }
public DateTime BillDate { get; set; }
public Guid CustomerId { get; set; }
public virtual Customer Customer { get; set; }
public decimal TotalAmount { get; set; }
public int Status { get; set; }
}
/// <summary>
/// 客户信息
/// </summary>
public class Customer
{
public Guid Id { get; set; }
public string Name { get; set; }
public string Area { get; set; }
}
那么我们这里使用的查询条件可能就会写成如下形式:
var exp=EFExpression<OrderMain>.CreateBinaryExpression(o=>o.Status,EBinaryType.Equal,0); //还没有送货 exp&=EFExpression<OrderMain>.CreateBinaryExpression(o=>o.TotalAmount ,EBinaryType.LessThan,500000); //小于50W var exp2=EFExpression<OrderMain>.CreateBinaryExpression(o=>o.Status,EBinaryType.Equal,1); //送货中 exp2&=EFExpression<OrderMain>.CreateBinaryExpression(o=>o.Customer.Area,EBinaryType.Equal,”0755”); //地址在深圳片区 exp|=exp2; var queryExpression=exp.GetExpression();
测试通过.
/// <summary>
/// 在当前条件基础上,构建一个like条件,并且和当前条件产生And运算
/// </summary>
/// <param name="property"></param>
/// <param name="val"></param>
/// <returns></returns>
public static EFExpression<T> AndLike<T>(this EFExpression<T> old, Expression<Func<T, string>> property, string val) where T : class
{
var temp = new LikeEFExpression<T>(property, val);
if (old == null)
return temp;
else
return new LogicEFExpression<T>(old, ELogicType.And, temp);
}
/// <summary>
/// 在当前条件基础上,构建一个等于条件,并且和当前条件产生And运算
/// </summary>
/// <typeparam name="TVal"></typeparam>
/// <param name="old"></param>
/// <param name="property"></param>
/// <param name="val"></param>
/// <returns></returns>
public static EFExpression<T> AndEqual<T, TVal>(this EFExpression<T> old, Expression<Func<T, TVal>> property, TVal val)
where TVal : IComparable
where T : class
{
var temp = new BinanryEFExpression<T, TVal>(property, EBinaryType.Equal, val);
if (old == null)
return temp;
else
return new LogicEFExpression<T>(old, ELogicType.And, temp);
}
/// <summary>
/// 在当前条件基础上,构建一个大于条件,并且和当前条件产生And运算
/// </summary>
/// <typeparam name="TVal"></typeparam>
/// <param name="old"></param>
/// <param name="property"></param>
/// <param name="val"></param>
/// <returns></returns>
public static EFExpression<T> AndGreaterThan<T, TVal>(this EFExpression<T> old, Expression<Func<T, TVal>> property, TVal val)
where TVal : IComparable
where T : class
{
var temp = new BinanryEFExpression<T, TVal>(property, EBinaryType.GreaterThan, val);
if (old == null)
return temp;
else
return new LogicEFExpression<T>(old, ELogicType.And, temp);
}
那么我们在使用的时候就可以方便的写成下面这种形式
var exp=EFExpression<OrderMain>.Create().AndEqual(o=>o.Status,0).AndGreaterThan(o=>o.TotalAmount ,500000)…..
在此不再赘述,有兴趣的朋友们可以自己去写出类似的东东,或问我要源码包...