Question

[sm2017]

Are the following codes same?

$promise= $deferred->promise()
    ->then(function () {
          // Logic codes
    })
    ->then(function () {
          // Logic codes
    })
    ->then(function () {
          // Logic codes
    });

And

$promise= $deferred->promise()
    ->then(function () {
          // Logic codes
    });
$promise->then(function () {
          // Logic codes
    });
$promise->then(function () {
          // Logic codes
    });

[jsor]

No, it is not the same. Chaining then() calls allows for transformation of the resolution value. See https://github.com/reactphp/promise/blob/master/README.md#resolution-forwarding.

$promise = $deferred->promise()
    ->then(function ($x) {
          // Here we get the initial resolution value: $x === 1;
          // Now add 1
          return $x + 1;
    })
    ->then(function ($x) {
          // Here we get the transformed value from the previous then() callback: $x === 2;
          // Now add 1 again
          return $x + 1;
    })
    ->then(function ($x) {
          // Here we get the transformed value from the previous then() callback: $x === 3;
          echo $x;
    });

$deferred->resolve(1);

[sm2017]

How exactly this code runs?

$promise = $deferred->promise();
$promise->then(function ($x) {
          // Here we get the initial resolution value: $x === 1;
          // Now add 1
          return $x + 1;
    });
$promise->then(function ($x) {
          // Here we get the transformed value from the previous then() callback: $x === 2;
          // Now add 1 again
          return $x + 1;
    });
$promise->then(function ($x) {
          // Here we get the transformed value from the previous then() callback: $x === 3;
          echo $x;
    });

$deferred->resolve(1);

How can I have a conditional then ?

Get a promise
Check redis , if found cached data , use it 
Else Fetch a row from database and then If(0<expireTime) then cache it to redis
then ...

[jsor]

How exactly this code runs?

This code doesn't chain promises but creates 3 new independent promises. In this case $x === 1 in all 3 callbacks.

How can I have a conditional then ?

Get a promise
Check redis , if found cached data , use it 
Else Fetch a row from database and then If(0<expireTime) then cache it to redis
then ...

Something like this maybe:

function fetchFromDbAndStoreToRedis($key)
{
    return queryDb($key)
        ->then(function($row) use ($key) {
            $value = $row['value'];

            if ($row['expireTime'] <= 0) {
                return $value;
            }

            return storeToRedis($key, $value, $row['expireTime'])
                ->then(function() use ($value) {
                    return $value;
                });
        })
    ;
}

fetchFromRedis($key)
    ->then(function($value) use ($key) {
        if (null !== $value) {
            return $value;
        }

        return fetchFromDbAndStoreToRedis($key);
    })
;

[jsor]

Closing for now, feel free to reopen if you have further questions.