表达式目录树的应用
1.使用表达式目录树实现两个不同类型的属性赋值：
首先，准备两个实体类
/// <summary>
/// 实体类
/// </summary>
public class People
{
public int Age { get; set; }
public string Name { get; set; }
public int Id;
}
/// <summary>
/// 实体类Target
/// PeopleDTO
/// </summary>
public class PeopleCopy
{
public int Age { get; set; }
public string Name { get; set; }
public int Id;
}接着写，数据处理类
/// <summary>
/// 生成表达式目录树 泛型缓存
/// </summary>
/// <typeparam name="TIn"></typeparam>
/// <typeparam name="TOut"></typeparam>
public class ExpressionGenericMapper<TIn, TOut>//Mapper`2
{
private static Func<TIn, TOut> _FUNC = null;
static ExpressionGenericMapper()
{
ParameterExpression parameterExpression = Expression.Parameter(typeof(TIn), "p");
List<MemberBinding> memberBindingList = new List<MemberBinding>();
foreach (var item in typeof(TOut).GetProperties())
{
MemberExpression property = Expression.Property(parameterExpression, typeof(TIn).GetProperty(item.Name));
MemberBinding memberBinding = Expression.Bind(item, property);
memberBindingList.Add(memberBinding);
}
foreach (var item in typeof(TOut).GetFields())
{
MemberExpression property = Expression.Field(parameterExpression, typeof(TIn).GetField(item.Name));
MemberBinding memberBinding = Expression.Bind(item, property);
memberBindingList.Add(memberBinding);
}
MemberInitExpression memberInitExpression = Expression.MemberInit(Expression.New(typeof(TOut)), memberBindingList.ToArray());
Expression<Func<TIn, TOut>> lambda = Expression.Lambda<Func<TIn, TOut>>(memberInitExpression, new ParameterExpression[]
{
parameterExpression
});
_FUNC = lambda.Compile();//拼装是一次性的
}
public static TOut Trans(TIn t)
{
return _FUNC(t);
}
}最后，程序中调用该代码处理
Stopwatch watch = new Stopwatch();
watch.Start();
for (int i = 0; i < 1_000_000; i++)
{
PeopleCopy peopleCopy = ExpressionGenericMapper<People, PeopleCopy>.Trans(people);
}
watch.Stop();
generic = watch.ElapsedMilliseconds;2. 使用表达式目录树，拼装sql语句
internal static class SqlOperator
{
internal static string ToSqlOperator(this ExpressionType type)
{
switch (type)
{
case (ExpressionType.AndAlso):
case (ExpressionType.And):
return "AND";
case (ExpressionType.OrElse):
case (ExpressionType.Or):
return "OR";
case (ExpressionType.Not):
return "NOT";
case (ExpressionType.NotEqual):
return "<>";
case ExpressionType.GreaterThan:
return ">";
case ExpressionType.GreaterThanOrEqual:
return ">=";
case ExpressionType.LessThan:
return "<";
case ExpressionType.LessThanOrEqual:
return "<=";
case (ExpressionType.Equal):
return "=";
default:
throw new Exception("不支持该方法");
}
}
} public static class ExpressionExtension
{
public static void BatchDelete<T>(this IQueryable<T> entities, Expression<Func<T, bool>> expr)
{
ConditionBuilderVisitor visitor = new ConditionBuilderVisitor();
visitor.Visit(expr);
string condition = visitor.Condition();
string sql = string.Format("DELETE FROM [{0}] WHERE {1};"
, typeof(T).Name//有可能还得根据泛型去获取
, condition);
//然后执行sql
}
}3， 合并表达式
/// <summary>
/// 合并表达式 And Or Not扩展
/// </summary>
public static class ExpressionExtend
{
/// <summary>
/// 合并表达式 expr1 AND expr2
/// </summary>
/// <typeparam name="T"></typeparam>
/// <param name="expr1"></param>
/// <param name="expr2"></param>
/// <returns></returns>
public static Expression<Func<T, bool>> And<T>(this Expression<Func<T, bool>> expr1, Expression<Func<T, bool>> expr2)
{
//return Expression.Lambda<Func<T, bool>>(Expression.AndAlso(expr1.Body, expr2.Body), expr1.Parameters);
if (expr1 == null)
return expr2;
else if (expr2 == null)
return expr1;
ParameterExpression newParameter = Expression.Parameter(typeof(T), "c");
NewExpressionVisitor visitor = new NewExpressionVisitor(newParameter);
var left = visitor.Replace(expr1.Body);
var right = visitor.Replace(expr2.Body);
var body = Expression.And(left, right);
return Expression.Lambda<Func<T, bool>>(body, newParameter);
}
/// <summary>
/// 合并表达式 expr1 or expr2
/// </summary>
/// <typeparam name="T"></typeparam>
/// <param name="expr1"></param>
/// <param name="expr2"></param>
/// <returns></returns>
public static Expression<Func<T, bool>> Or<T>(this Expression<Func<T, bool>> expr1, Expression<Func<T, bool>> expr2)
{
if (expr1 == null)
return expr2;
else if (expr2 == null)
return expr1;
ParameterExpression newParameter = Expression.Parameter(typeof(T), "c");
NewExpressionVisitor visitor = new NewExpressionVisitor(newParameter);
var left = visitor.Replace(expr1.Body);
var right = visitor.Replace(expr2.Body);
var body = Expression.Or(left, right);
return Expression.Lambda<Func<T, bool>>(body, newParameter);
}
public static Expression<Func<T, bool>> Not<T>(this Expression<Func<T, bool>> expr)
{
if (expr == null) return null;
var candidateExpr = expr.Parameters[0];
var body = Expression.Not(expr.Body);
return Expression.Lambda<Func<T, bool>>(body, candidateExpr);
}
}方法调用
Expression<Func<People, bool>> lambda1 = x => x.Age > 5;
Expression<Func<People, bool>> lambda2 = x => x.Id > 5;
Expression<Func<People, bool>> lambda3 = lambda1.And(lambda2);
Expression<Func<People, bool>> lambda4 = lambda1.Or(lambda2);
Expression<Func<People, bool>> lambda5 = lambda1.Not();
Do1(lambda3);
Do1(lambda4);
Do1(lambda5);本文参与?腾讯云自媒体分享计划，分享自作者个人站点/博客。
原始发表：2020-03-04，如有侵权请联系 cloudcommunity@tencent.com 删除
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