動態Linq表達式用於多級查詢

Question

我有以下要動態構建的Linq表達式。

我遇到的問題是我無法構建表達式樹來容納復雜的Select / Any語句。 我讀過，為了使用方法，您必須按如下方式調用該方法：

 Invoke("Any")

---

我需要動態構建的表達式：

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();

這是我的模型類：

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; }

    ...
}

---

OLifE

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; }

    ...
}

---

RequirementInfo

public partial class RequirementInfo : BaseEntity
{
     public virtual OLI_LU_REQSTAT ReqStatus { get; set; }

    ...
}   

---

目前，我正在針對GetProperty運行反射foreach，但無法理解文檔以使對象模型降低3-4級：

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。 添加所有的類屬性沒有意義，因為那里存在所需的類結構。

Answer 1

相當長。 我覺得“維護”太復雜了，如果您需要進行一些更改，這將變得非常困難。 甚至使其成為“動態的”以便可以對其進行控制（啟用或禁用零件）也是困難的。

特定

// 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();

分別是LINQ Enumerable.Any()和Enumerable.Select()

並給了你

// 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();

將您的表情與生成的表情進行比較

使用一些快捷方式（而不是txreq.IsDeleted == False我使用!rxreq.IsDeleted ，而不是包括OLI_LU_REQSTAT.OLI_REQSTAT_OUTSTANDING.tc我在構建表達式樹時讀取了它的值並將其放在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();

如果我們嘗試lambda.ToString()我們得到：

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

足夠類似了。