C# EF 字符串模糊查詢完整實例 lambda

判斷是否為null
whereExpression = p =>string.IsNullOrWhiteSpace(p.RealName)
等同於
SELECT * FROM tbl WHERE RealNameIS NULL

判斷以什么開頭，前綴匹配
whereExpression = p =>p.RealName.StartsWith("AA")
等同於
SELECT * FROM tbl WHERE RealName like 'AA%'

判斷以什么結尾，后綴匹配

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

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

其他自定義特殊 查詢

var pattern = $"______{str}%"; //‘_’ like中的占位符 此處查詢第7位為指定字符的數據,str為變量
whereExpression = p => SqlFunctions.PatIndex(pattern, p.RealSampleNo) > 0

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

** 長度查詢 **
whereExpression = p =>p.RealName.Length==1
** 字節長度查詢 **
whereExpression = p =>SqlFunctions.DataLength(p.RealName)==8