LINQ大于/小于在查询中不起作用 [英] LINQ greater/less than not working in query

问题描述

var query = db.Products.Where(p => p.Cost == 10M); 可以很好地工作并返回正确的结果列表. var query = db.Products.Where(p => p.Cost> 10M); 引发异常:

var query = db.Products.Where(p => p.Cost == 10M); works perfectly fine and returns the correct list of results. var query = db.Products.Where(p => p.Cost > 10M); throws an exception:

LINQ表达式'DbSet< Product> .Where(p => p.Cost>(Nullable< decimal>)10)'无法翻译.

很明显，C#生成的脚本无法在SQL中执行，但是为什么不呢?那是有效的SQL查询

Obviously the script being generated by C# can't be executed in SQL but why not? That is a valid SQL query

public class Product
    {
        public int ProductID {get;set;}
        [Required]
        [StringLength(40)]
        public string ProductName {get;set;}
        [Column("UnitPrice", TypeName="money")]
        public decimal? Cost {get;set;}
    }

    public class Northwind: DbContext
    {
        public DbSet<Category> Categories {get;set;}
        public DbSet<Product> Products {get;set;}
    }

EFCore 3.1.2，.NET Core 3.1.1

EFCore 3.1.2, .NET Core 3.1.1

推荐答案

看起来 p.Cost 是一个十进制?.在这种情况下，您可以使用 null合并运算符.

It looks like p.Cost is a decimal?. In that case you can use the null coalescing operator.

var query = db.Products.Where(p => (p.Cost ?? 0) > 10M);

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