Wait for current loop in for loop to finish, before continuing

Question

What is the best way to make javascript wait for the current iteration of the for loop to finish before the next one?

Heres my problem.

At the moment, I am running an SQL select statement from a SQLite database for each item in a for loop, like this.

for(let i = 0; i < myresult.length; i++){
    var query = "SELECT * FROM table WHERE id = " + myresult[i].id;
    var result = //Run sql here    
    if(result.length == 0){ // if result doesn't exist, make it.
       var insertQuery = "INSERT INTO table";
    }
}

My issue is that as it runs through the loop, it starts to run the insert statement before the select is complete.

For example

//First iteration of loop

"SELECT * FROM table WHERE id = 1";

"INSERT INTO table (id) VALUES (1)";

//Second iteration of loop

"SELECT * FROM table WHERE id = 2";

"INSERT INTO table (id) VALUES (1)";

It is doing this because its not waiting for the current iteration of the for loop to finish, before starting the next.

How do I make it so that the for loop waits for the current loop to finish, before starting a new one?

The SQL queries are asynchronous. They probably have some promise or callback mechanism. — Ori Drori, Apr 05 '18 at 12:01
Sync would have blocked the thread, and you wouldn't have the problem. What are you using to connect to SQL? Browser or Node? — Ori Drori, Apr 05 '18 at 12:06
How is this line really executed? `var result = //Run sql here` ... if that one doesn't block until done, e.g. fire up an AJAX call, you'll end up with such issue. — Asons, Apr 05 '18 at 12:07
Maybe use a [generator](https://www.promisejs.org/generators/)? — zer00ne, Apr 05 '18 at 12:07
You omitted the most important line: var result = //Run sql here Please show your code. — Rob, Apr 05 '18 at 12:19
If I only had a dime every time this type of async questions were asked... — nicholaswmin, Apr 05 '18 at 12:35
Possible duplicate of [How do I return the response from an asynchronous call?](https://stackoverflow.com/questions/14220321/how-do-i-return-the-response-from-an-asynchronous-call) — nicholaswmin, Apr 05 '18 at 12:36

score -1 · Answer 1 · answered Apr 05 '18 at 12:25

It will be Better if you Use Store Procedure in ms-sql and bind your data in JSON on Javascript using ajax/angular.

DECLARE @TEMPTABLE TABLE (

                                              field1 BIGINT, -- ID
                                              field2 NVARCHAR(100), 
                                              field3 NVARCHAR(150), 
                                              field4 NVARCHAR(150) 
                     );

INSERT @tempTable (

          field1, 
          field2, 
          field3, 
          field4 
   )

SELECT t.field1,

   t.field2,

   t.field3, 

   t.field4

FROM table1 t

DECLARE @CountTable INT = (

   SELECT Count(*) 

   FROM   @tempTable t

);

IF (@CountTable <= 0)

BEGIN

SELECT 'NO RECORD FOUND' AS [STATUS];

RETURN;

END;

DECLARE @count INT;

SET @count = 1;

WHILE (@count <= @CountTable)

BEGIN

DECLARE @Field1 NVARCHAR(100) = '',

@Field2       NVARCHAR(150) = '', 
@Field3       NVARCHAR(150) = '', 
@Field4       NVARCHAR(150) = '',

select top 1

     @Field1 = t.field1, 
     @Field2 = t.field2, 
     @Field3 = t.field3, 
     @Field4 = t.field4

FROM @tempTable t;

DELETE @tempTable

WHERE field1 = @Field1; -- ID

SET @count = @count + 1; END;

Wait for current loop in for loop to finish, before continuing

1 Answers1