用于多级查询的动态 Linq 表达式

我想动态构建以下 Linq 表达式。

我遇到的问题是我无法构建表达式树来容纳复杂的 Select/Any 语句。我读过，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; }
}

TXLife请求

public partial class TXLifeRequest : BaseEntity
{
    public virtual OLifE OLifE { get; set; }

    ...
}

OLifE

public partial class OLifE : BaseEntity
{
    public virtual List<Holding> Holding { get; set; }
        ...
}

Holding

public class Holding : BaseEntity
{
    public virtual Policy Policy { get; set; }
    ...
}

Policy

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 foreach 反射，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。）添加了需求信息。添加所有类属性是没有意义的，因为所需的类结构已经存在。

相当长。我觉得它太复杂了，“可维护”，如果你需要做一些改变，那就变得相当困难。即使使其“动态”以便可以控制（启用或禁用部件）也是很困难的。

Given

// 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();

这就是 LINQEnumerable.Any() and 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 I use !rxreq.IsDeleted而不是包括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() we get:

txreq => (Not(txreq.IsDeleted) AndAlso txreq.OLifE.Holding.Select(h => h.Policy).Any(p => p.RequirementInfo.Any(r => (r.ReqStatus.tc == "SOMEVALUE"))))

这足够相似了。