c# - 用于多级查询的动态 Linq 表达式
问题描述
我有以下我想动态构建的 Linq 表达式。
我遇到的问题是我无法构建表达式树来适应复杂的 Select/Any 语句。我已经读过,为了使用方法,您实际上必须调用该方法,如下所示:
Invoke("Any")
我需要动态构建的表达式:
Expression<Func<TXLifeRequest, bool>> filter = (txreq) =>
txreq.IsDeleted == false &&
txreq.OLifE.Holding.Select(h => h.Policy)
.Any(p => p.RequirementInfo
.Any(r => r.ReqStatus.tc == OLI_LU_REQSTAT.OLI_REQSTAT_OUTSTANDING.tc));
var results = db.GetQueryable(filter)
.Include(r => r.OLifE.Holding.Select(h => h.Policy)
.Select(p => p.RequirementInfo)).ToList();
这是我的模型类:
OLI_LU_REQSTAT
public partial class OLI_LU_REQSTAT : BaseType {
public string tc { get; set; }
public string Value { get; set; }
}
TXLifeRequest
public partial class TXLifeRequest : BaseEntity
{
public virtual OLifE OLifE { get; set; }
...
}
生活
public partial class OLifE : BaseEntity
{
public virtual List<Holding> Holding { get; set; }
...
}
保持
public class Holding : BaseEntity
{
public virtual Policy Policy { get; set; }
...
}
政策
public class Policy : BaseEntity
{
public virtual List<RequirementInfo> RequirementInfo { get; set; }
...
}
需求信息
public partial class RequirementInfo : BaseEntity
{
public virtual OLI_LU_REQSTAT ReqStatus { get; set; }
...
}
目前我正在针对 GetProperty 运行反射 foreach 但无法理解文档以便在对象模型中降低 3-4 级:
ParameterExpression parameter = Expression.Parameter(typeof(T), "i");
MemberExpression property = Expression.Property(parameter, propertyName);
ConstantExpression constant = Expression.Constant(val, propertyType);
var condition =
Expression.Lambda<Func<T, bool>>(
Expression.Equal(
property,
constant
),
parameter
);
result = AppendExpression(result, condition, result);
更新 1.)添加了 RequirementInfo。添加所有类属性没有意义,因为所需的类结构已经存在。
解决方案
相当长。我觉得“可维护”太复杂了,如果你需要做一些改变,就变得相当困难。甚至使它“动态”以便可以控制(启用或禁用部分)也很困难。
给定
// Enumerable.Any()
static readonly MethodInfo anyTSource = (from x in typeof(Enumerable).GetMethods(BindingFlags.Static | BindingFlags.Public)
where x.Name == nameof(Enumerable.Any)
let args = x.GetGenericArguments()
where args.Length == 1
let pars = x.GetParameters()
where pars.Length == 2 &&
pars[0].ParameterType == typeof(IEnumerable<>).MakeGenericType(args[0]) &&
pars[1].ParameterType == typeof(Func<,>).MakeGenericType(args[0], typeof(bool))
select x).Single();
// Enumerable.Select()
public static readonly MethodInfo selectTSourceTResult = (from x in typeof(Enumerable).GetMethods(BindingFlags.Static | BindingFlags.Public)
where x.Name == nameof(Enumerable.Select)
let args = x.GetGenericArguments()
where args.Length == 2
let pars = x.GetParameters()
where pars.Length == 2 &&
pars[0].ParameterType == typeof(IEnumerable<>).MakeGenericType(args[0]) &&
pars[1].ParameterType == typeof(Func<,>).MakeGenericType(args[0], args[1])
select x).Single();
那是LINQEnumerable.Any()
和Enumerable.Select()
并给出你的
// txreq => ((txreq.IsDeleted == False) AndAlso txreq.OLifE.Holding.Select(h => h.Policy).Any(p => p.RequirementInfo.Any(r => (r.ReqStatus.tc == OLI_LU_REQSTAT.OLI_REQSTAT_OUTSTANDING.tc))))
string str1 = filter.ToString();
将您的表达式与生成的表达式进行比较
使用一些快捷方式(而不是txreq.IsDeleted == False
我使用!rxreq.IsDeleted
and 而不是包含OLI_LU_REQSTAT.OLI_REQSTAT_OUTSTANDING.tc
我在构建表达式树时读取它的值并将其放入Expression.Constant()
,
var par = Expression.Parameter(typeof(TXLifeRequest), "txreq");
// txreq.IsDeleted == false (simplified to !txreq.IsDeleted)
var notIsDeleted = Expression.Not(Expression.Property(par, "IsDeleted"));
// r =>
var par4 = Expression.Parameter(typeof(RequirementInfo), "r");
// OLI_LU_REQSTAT.OLI_REQSTAT_OUTSTANDING.tc
var oli_reqstat_outstanding_tc = Expression.Constant(OLI_LU_REQSTAT.OLI_REQSTAT_OUTSTANDING.tc);
// r.ReqStatus.tc == OLI_LU_REQSTAT.OLI_REQSTAT_OUTSTANDING.tc
Expression<Func<RequirementInfo, bool>> any2Lambda = Expression.Lambda<Func<RequirementInfo, bool>>(Expression.Equal(Expression.Property(Expression.Property(par4, "ReqStatus"), "tc"), oli_reqstat_outstanding_tc), par4);
// To check if it is correct
//any2Lambda.Compile();
// p =>
var par3 = Expression.Parameter(typeof(Policy), "p");
// p.RequirementInfo.Any(...)
Expression<Func<Policy, bool>> any1Lambda = Expression.Lambda<Func<Policy, bool>>(Expression.Call(anyTSource.MakeGenericMethod(typeof(RequirementInfo)), Expression.Property(par3, "RequirementInfo"), any2Lambda), par3);
// To check if it is correct
//any1Lambda.Compile();
// h =>
var par2 = Expression.Parameter(typeof(Holding), "h");
// h.Policy
Expression<Func<Holding, Policy>> selectLambda = Expression.Lambda<Func<Holding, Policy>>(Expression.Property(par2, "Policy"), par2);
// To check if it is correct
//selectLambda.Compile();
//txreq.OLifE.Holding
var holding = Expression.Property(Expression.Property(par, "OLifE"), "Holding");
// txreq.OLifE.Holding.Select(...)
var select = Expression.Call(selectTSourceTResult.MakeGenericMethod(typeof(Holding), typeof(Policy)), holding, selectLambda);
var any1 = Expression.Call(anyTSource.MakeGenericMethod(typeof(Policy)), select, any1Lambda);
var and = Expression.AndAlso(notIsDeleted, any1);
Expression<Func<TXLifeRequest, bool>> lambda = Expression.Lambda<Func<TXLifeRequest, bool>>(and, par);
// To check if it is correct and/or use it
//var compiled = lambda.Compile();
如果我们尝试lambda.ToString()
,我们会得到:
txreq => (Not(txreq.IsDeleted) AndAlso txreq.OLifE.Holding.Select(h => h.Policy).Any(p => p.RequirementInfo.Any(r => (r.ReqStatus.tc == "SOMEVALUE"))))
这已经足够相似了。
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