vb.net - 在 linq 中搜索多个列

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，如果任何字段为空白或什么都没有，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

桌子

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，但这不会取回任何数据

(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

我还需要将此限制为 250 条记录

提前感谢保罗

Answer 1

您的每个字符串检查还应检查该值是否不是空字符串 ("")。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