Question

我是linq的新手。我正在尝试编写一个linq查询，它将搜索数据库中的3个字段。但是，如果任何字段为空或无，则它不会在查询中包含该字段。

搜索对象

Public Class Search
    Public Property firstName As String
    Public Property surname As String
    Public Property address As String
End Class

表

CREATE TABLE [dbo].[user] (
[id] [int] IDENTITY(1,1) NOT NULL,
[firstName] [nvarchar](50) NULL,
[surname] [nvarchar](50) NULL,
[fullAddress] [nvarchar](1050) NULL

我的尝试，但这不会得到任何数据

(From it In db.user 
 Where (
     searchItems.firstName IsNot Nothing 
     AndAlso it.firstName.Contains(searchItems.firstName)) 
 AndAlso (searchItems.surname IsNot Nothing 
     AndAlso it.surname.Contains(searchItems.surname)) 
 AndAlso (searchItems.address IsNot Nothing 
     AndAlso it.fullAddress.Contains(searchItems.address)) 
 Select it).
 ToList

此外，我需要将此限制为250条记录

提前致谢保罗

Answer 1

每个字符串检查还应检查该值是否为空字符串（“”）。如果您为每个字符串检查添加额外的检查，您应该能够完成此操作，例如：

(From it In db.user 
 Where (Not String.IsNullOrEmpty(searchItems.firstName)) Or (it.firstName.Contains(searchItems.firstName))
 AndAlso (Not String.IsNullOrEmpty(searchItems.surname) Or (it.surname.Contains(searchItems.surname)) 
 AndAlso (Not String.IsNullOrEmpty(searchItems.address) Or (it.fullAddress.Contains(searchItems.address)) 
 Select it).Take(250).ToList

在linq中搜索多个列

1 个答案: