檢查Dapper是否存在記錄ORM

Question

使用Dapper ORM檢查記錄是否存在的最簡單方法是什麼？

我真的需要爲查詢定義POCO對象嗎？我只想檢查記錄是否存在？

Answer 1

int id = ... 
var exists = conn.ExecuteScalar<bool>("select count(1) from Table where Id=@id", new {id}); 

應該工作...

Answer 2

你可以有你的查詢返回一個bool：

[Test] 
    public void TestExists() 
    { 
     var sql = @"with data as 
        (
         select 1 as 'Id' 
        ) 
        select CASE WHEN EXISTS (SELECT Id FROM data WHERE Id = 1) 
          THEN 1 
          ELSE 0 
         END AS result 
        from data "; 

     var result = _connection.Query<bool>(sql).FirstOrDefault(); 

     Assert.That(result, Is.True); 
    } 

Answer 3

我覺得這可能有一點點的開銷更少，因爲沒有函數調用或數據類型轉換：

int id = ... 
var exists = connection.Query<object>(
    "SELECT 1 WHERE EXISTS (SELECT 1 FROM MyTable WHERE ID = @id)", new { id }) 
    .Any(); 

Answer 4

另一個選項將運行重複記錄，即不查詢表格的ID Ë

bool exists = connection.ExecuteScalar<int>(
    "select count(1) from Table where notanId=@value", new { value = val}) 
    > 0; 

Answer 5

const string sql = "SELECT CAST(CASE WHEN EXISTS (SELECT 1 FROM MyTable WHERE Id = @Id) THEN 1 ELSE 0 END as BIT)"; 
bool exists = db.ExecuteScalar<bool>(sql, new { Id = 123 });