为什么LINQ生成的SQL包含多个“IS NULL"?同一列的条件
以下针对 SQL Server 2012 数据库的查询,使用 Entity Framework Core 3.1:
The following query against a SQL Server 2012 database, using Entity Framework Core 3.1:
var tows = await _context.DataEntryTow
.Where(t => _context.DataEntrySample
.Any(s => s.TowId==t.TowId && (s.MicroscopeId != "0" || s.MicroscopeId == null)))
.Select (t => new { text = t.TowId, value = t.TowId });
生成此 SQL:
SELECT d.tow_id AS text
FROM data_entry_tow AS d
WHERE EXISTS (
SELECT 1
FROM data_entry_sample AS d0
WHERE (d0.tow_id = d.tow_id) AND (((d0.microscope_id <> '0') OR (d0.microscope_id IS NULL)) OR (d0.microscope_id IS NULL)))
我不认为我做错了什么,我相当确定查询优化器会消除第二个(d0.microscope_id IS NULL)
,但它似乎仍然是 LINQ 代码中的错误.
I don't think I've done anything wrong, and I'm fairly sure the query optimizer will eliminate the second (d0.microscope_id IS NULL)
, but it still seems like an error in the LINQ code.
MicroscopeId 已定义:
public string MicroscopeId { get; set; }
推荐答案
Field MicroscopeId
声明为可为空.因此,当 null != "0"
为 true
但在 SQL null <> 中时,要模仿 LINQ to Objects 的行为.'0'
为假,EF Core 生成额外的 OR
条件.
Field MicroscopeId
declared as nullable. So, to mimic LINQ to Objects behaviour when null != "0"
is true
but in SQL null <> '0'
is false, EF Core generates additional OR
condition.
要禁用此生成,您必须在构建 DbContextOptions 时指定:
To disable this geneeration you have to specify that when building DbContextOptions:
optionsBuilder.UseSqlServer(constr, b => b.UseRelationalNulls(true) );
附加信息:https://docs.microsoft.com/en-us/ef/core/querying/null-comparisons#using-relational-null-semantics
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