構建從linq到ef核心的動態where查詢

我的模型如下所示

public class Country
{
  public int Id {get; set;}
  public string Name {get; set;}
}

public class User
{
 public int Id{get; set;}
 public string FirstName {get; set;}
 public string LastName {get; set;}
 public string Email {get; set;}
}

public class Company
{
  public int Id{get; set;}
  public string Name {get;set;}
  public string City {get; set;}
  public string Address1 {get; set;}
  public string Address2 {get; set;}
  [ForeignKey("Country")]
  public int CountryId{get; set;}

  public Country Country{get; set;}
  public ICollection<CompanyUsers> CompanyUsers {get; set;}
}

public class CompanyUsers
{
 public int Id{get; set;}
 [ForeignKye("Company")]
 public int CompanyId {get; set;}
 [ForeignKye("User")]
 public int UserId {get; set;}

 public Country Country{get; set;}
 public User User{get; set;}
}

我想讓用戶能夠通過Country, Company or User class 除了 Id 屬性中定義的任何屬性來搜索公司記錄

我嘗試查看此SO 討論，但它不處理導航屬性。有人可以幫助我構建動態 where 子句，包括導航屬性中的屬性。

有了這個實作，我只能做如下

myContext.CompanyEntity
.Where(FilterLinq<CompanyEntity>
.GetWherePredicate(searchParams))
.ToList();

public class SearchField
{
  public string Key { get; set; }
  public string Value { get; set; }
}

uj5u.com熱心網友回復：

從您指出的答案擴展這個想法并不復雜。

您需要更改假設，以便 SerchField 中的屬性名稱可以包含屬性路徑的定義，例如Company.CityorCompany.Country.Name以及 property FirstName。你需要處理它：

所以不僅僅是像這樣簡單的屬性：

Expression columnNameProperty = Expression.Property(pe, fieldItem.Name);

你需要處理財產鏈：

Expression columnNameProperty = GetPropertyExpression(pe, fieldItem.Name);


Expression GetPropertyExpression(Expression pe, string chain){
    var properties = chain.Split('.');
    foreach(var property in properties)
          pe = Expression.Property(pe, property);

    return pe;
}

基本上，這段代碼的作用是pe在創建屬性鏈的每個回圈上應用屬性而不是先前的修改變數。物體框架將處理它并創建適當的連接。這僅適用于單個關系，不適用于集合。

因此該答案的修改后的代碼如下所示：

public class FilterLinq<T>
{
    Expression GetPropertyExpression(Expression pe, string chain)
    {
        var properties = chain.Split('.'); 
        foreach(var property in properties)
           pe = Expression.Property(pe, property);

        return pe;
    }

    public static Expression<Func<T, Boolean>> GetWherePredicate(params SearchField[] SearchFieldList)
    {

        //the 'IN' parameter for expression ie T=> condition
        ParameterExpression pe = Expression.Parameter(typeof(T), typeof(T).Name);

        //combine them with and 1=1 Like no expression
        Expression combined = null;

        if (SearchFieldList != null)
        {
            foreach (var fieldItem in SearchFieldList)
            {
                //Expression for accessing Fields name property
                Expression columnNameProperty = GetPropertyExpression(pe, fieldItem.Name);

                //the name constant to match 
                Expression columnValue = Expression.Constant(fieldItem.Value);

                //the first expression: PatientantLastName = ?
                Expression e1 = Expression.Equal(columnNameProperty, columnValue);

                if (combined == null)
                {
                    combined = e1;
                }
                else
                {
                    combined = Expression.And(combined, e1);
                }
            }
        }

        //create and return the predicate
        return Expression.Lambda<Func<T, Boolean>>(combined, new ParameterExpression[] { pe });
    }

}

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