问题描述
使用 universal PredicateBuilder 可以在不链接到 DbSet 的情况下构建谓词。例如我有课
public class Сountry
{
public int Id { get; set; }
public bool IsSchengen { get; set; }
}
public class Institute
{
public int Id { get; set; }
public int CountryId { get; set; }
public bool IsNational { get; set; }
public string Title { get; set; }
}
使用 PredicateBuilder 构建谓词:
public static Expression<Func<Institute,bool>> BuilPredicate(bool isNational)
{
var predicate = new PredicateBuilder<Institute>()
.And(ao => ao.IsNational == isNational);
return predicate.Build();
}
现在我需要按国家过滤研究所:
public static Expression<Func<Institute,bool>> BuilPredicate(
bool isNational,bool countryIsSchengen,DbContext db) // <== don't want to pass link to DbContext
{
var predicate = new PredicateBuilder<Institute>()
.And(ii => ii.IsNational == isNational);
// filter by countries
// question: how to make the same without DbContext
var countyIds = db.Set<Сountry>()
.Where(cc => cc.IsSchengen == countryIsSchengen)
.Select(cc => cc.Id);
predicate.And(ii => countyIds.Contains(ii.CountryId));
return predicate.Build();
}
是否可以在不链接到 DbContext 的情况下创建这样的谓词? 并且没有导航国家属性:
public class Institute
{
public int Id { get; set; }
// without this
// public Country Country { get; set; }
public int CountryId { get; set; }
public bool IsNational { get; set; }
public string Title { get; set; }
}
解决方法
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