C# EF 字符串模糊查询完整实例 lambda

Posted 2021-12-07 大雄

判断是否为null
whereExpression = p =>string.IsNullOrWhiteSpace(p.RealName)
等同于
SELECT * FROM tbl WHERE RealNameIS NULL

判断以什么开头，前缀匹配
whereExpression = p =>p.RealName.StartsWith("AA")
等同于
SELECT * FROM tbl WHERE RealName like \'AA%\'

判断以什么结尾，后缀匹配

whereExpression = p =>p.RealName.EndWith("AA")
等同于
SELECT * FROM tbl WHERE RealName like \'%AA\'

包含查询
whereExpression = p =>p.RealName.Contains("AA")
等同于
SELECT * FROM tbl WHERE RealName like \'%AA%\'

其他自定义特殊 查询

var pattern = $"______{str}%"; //‘_’ like中的占位符 此处查询第7位为指定字符的数据,str为变量
whereExpression = p => SqlFunctions.PatIndex(pattern, p.RealSampleNo) > 0

等同于
SELECT * FROM tbl WHERE RealName like \'______{str}%\'

** 长度查询 **
whereExpression = p =>p.RealName.Length==1
** 字节长度查询 **
whereExpression = p =>SqlFunctions.DataLength(p.RealName)==8