题
我有以下函数，它实际上是Z.EntityFramework.Plus批量更新的包装器：
public static int UpdateBulk<T>(this IQueryable<T> query, Expression<Func<T, T>> updateFactory) where T : IBaseEntity, new()
{
Expression<Func<T, T>> modifiedExpression = x => new T() { ModifiedBy = "Test", ModifiedDate = DateTime.Now };
var combine = Expression.Lambda<Func<T, T>>(
Expression.AndAlso(
Expression.Invoke(updateFactory, updateFactory.Parameters),
Expression.Invoke(modifiedExpression, modifiedExpression.Parameters)
),
updateFactory.Parameters.Concat(modifiedExpression.Parameters)
); //This returns an error
return query.Update(combine);
}
这样称呼：
public static int UpdateBulk<T>(this IQueryable<T> query, Expression<Func<T, T>> updateFactory) where T : IBaseEntity, new()
{
Expression<Func<T, T>> modifiedExpression = x => new T() { ModifiedBy = "Test", ModifiedDate = DateTime.Now };
var combine = Expression.Lambda<Func<T, T>>(
Expression.AndAlso(
Expression.Invoke(updateFactory, updateFactory.Parameters),
Expression.Invoke(modifiedExpression, modifiedExpression.Parameters)
),
updateFactory.Parameters.Concat(modifiedExpression.Parameters)
); //This returns an error
return query.Update(combine);
}
IBaseEntity的定义如下：
public static int UpdateBulk<T>(this IQueryable<T> query, Expression<Func<T, T>> updateFactory) where T : IBaseEntity, new()
{
Expression<Func<T, T>> modifiedExpression = x => new T() { ModifiedBy = "Test", ModifiedDate = DateTime.Now };
var combine = Expression.Lambda<Func<T, T>>(
Expression.AndAlso(
Expression.Invoke(updateFactory, updateFactory.Parameters),
Expression.Invoke(modifiedExpression, modifiedExpression.Parameters)
),
updateFactory.Parameters.Concat(modifiedExpression.Parameters)
); //This returns an error
return query.Update(combine);
}
顺便说一句，“问题”类实现了IBaseEntity。
我想要做的是自动将ModifiedBy和ModifiedDate附加到UpdateBulk函数中的updateFactory，这样就不必在每次调用UpdateBulk时都这样做。
我尝试在上面的UpdateBulk函数中将解析后的'updateFactory'表达式与'modifiedExpression'结合起来，但它返回错误：
二元运算符AndAlso没有为类型'问题'定义
是否有可能像这样合并Expression，如果是这样，我做错了什么？如果没有，我如何将ModifiedBy =“Test”，ModifiedDate = DateTime.Now合并到updateFactory表达式中？
谢谢，罗德
一般承认的答案
你不能使用AndAlso ，因为那意味着BinaryExpression - Expression<Func<T,bool>> ，在这种情况下你需要表达式访问者， 这里由Marc Gravell定义（因此他值得所有的功劳）
我正在使用相同的方法在您的情况下提供解决方案，假设有Problem class schema ，粘贴Linqpad代码：
void Main()
{
var final = UpdateBulk((Problem p) => new Problem{CatId = 1,SubCatId = 2, ListId=3});
// final is of type Expression<Func<T,T>>, which can be used for further processing
final.Dump();
}
public static Expression<Func<T, T>> UpdateBulk<T>(Expression<Func<T, T>> updateFactory) where T : IBaseEntity, new()
{
Expression<Func<T, T>> modifiedExpression = x => new T() { ModifiedBy = "Test", ModifiedDate = DateTime.Now };
var result = Combine(updateFactory, modifiedExpression);
return result;
}
static Expression<Func<TSource, TDestination>> Combine<TSource, TDestination>(
params Expression<Func<TSource, TDestination>>[] selectors)
{
var param = Expression.Parameter(typeof(TSource), "x");
return Expression.Lambda<Func<TSource, TDestination>>(
Expression.MemberInit(
Expression.New(typeof(TDestination).GetConstructor(Type.EmptyTypes)),
from selector in selectors
let replace = new ParameterReplaceVisitor(
selector.Parameters[0], param)
from binding in ((MemberInitExpression)selector.Body).Bindings
.OfType<MemberAssignment>()
select Expression.Bind(binding.Member,
replace.VisitAndConvert(binding.Expression, "Combine")))
, param);
}
class ParameterReplaceVisitor : ExpressionVisitor
{
private readonly ParameterExpression from, to;
public ParameterReplaceVisitor(ParameterExpression from, ParameterExpression to)
{
this.from = from;
this.to = to;
}
protected override Expression VisitParameter(ParameterExpression node)
{
return node == from ? to : base.VisitParameter(node);
}
}
public abstract class IBaseEntity
{
public System.DateTime CreatedDate { get; set; }
public string CreatedBy { get; set; }
public System.DateTime ModifiedDate { get; set; }
public string ModifiedBy { get; set; }
public string DeletedBy { get; set; }
}
public class Problem : IBaseEntity
{
public int CatId { get; set; }
public int SubCatId { get; set; }
public int ListId { get; set; }
}