# Help using list in UDF

**URL:** <https://discuss.aerospike.com/t/help-using-list-in-udf/996>\
**Category:** User Defined Functions (UDF)\
**Created:** [March 1, 2015, 8:18am UTC](https://discuss.aerospike.com/t/help-using-list-in-udf/996 "2015-03-01T08:18:53Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![n\_k](https://avatars.discourse-cdn.com/v4/letter/n/c68b51/32.png) [@n\_k](https://discuss.aerospike.com/u/n_k)\
**Post date:** [March 1, 2015, 8:18am UTC](https://discuss.aerospike.com/t/help-using-list-in-udf/996/1 "2015-03-01T08:18:53Z")

</div>

Hi,

I’m trying to maintain a list of strings.

This is my code when I create a record:

```
local function initRecord(record)
    if(not aerospike:exists(record)) then
        record.backlog = list()
        for i=1,3, 1 do
            local val = 'n/a'
            record.backlog[i] = val
        end
        local rc = 0;
        rc = aerospike:create(record)
        if( rc == nil or record == nil ) then
            error("Could not create record")
        end
    end
end

```

And it works fine (bins:(backlog:[n/a, n/a, n/a]), but when I want to modify this list, it does not seam to do anything with any of the following methods:

```
local function pushToBacklog(record, requestId)
    list.append(record.backlog, requestId)
    aerospike:update(record)
end

```

or

```
local function pushToBacklog(record, requestId)
    record.backlog[1] = requestId
    aerospike:update(record)
end

```

Any idea?

---

<div class="post-metadata">

**Author:** ![helipilot50](https://sea1.discourse-cdn.com/flex019/user_avatar/discuss.aerospike.com/helipilot50/32/59_2.png) [@helipilot50](https://discuss.aerospike.com/u/helipilot50)\
**Post date:** [March 2, 2015, 1:19am UTC](https://discuss.aerospike.com/t/help-using-list-in-udf/996/2 "2015-03-02T01:19:12Z")

</div>

Hi

Try adding the following code just before you call aerospike:update(…)

```
record.backlog = record.backlog

```

It seems a bit strange, but I’ll explain. To Lua, the Aerospike record “looks” like a table, and you can operate on it like you would a table; cstivers78 did a great job on implementing this.

Here is the secret: For Aerospike to know that the bin needs to be updated, the bin needs to be “touched”. You are adding to a list in the UDF, which is OK, but the Bin containing a pointer to the list has not been modified, or “touched”. So assigning the bin to itself should work.

Regards,

Peter

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<div class="post-metadata">

**Author:** ![n\_k](https://avatars.discourse-cdn.com/v4/letter/n/c68b51/32.png) [@n\_k](https://discuss.aerospike.com/u/n_k)\
**Post date:** [March 3, 2015, 10:02am UTC](https://discuss.aerospike.com/t/help-using-list-in-udf/996/3 "2015-03-03T10:02:34Z")

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> [@helipilot50](#):
>
> record.backlog = record.backlog

Thanks! This works fine now.

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**Author:** ![ManuelSchmidt](https://sea1.discourse-cdn.com/flex019/user_avatar/discuss.aerospike.com/manuelschmidt/32/424_2.png) [@ManuelSchmidt](https://discuss.aerospike.com/u/ManuelSchmidt)\
**Post date:** [January 31, 2016, 11:37am UTC](https://discuss.aerospike.com/t/help-using-list-in-udf/996/4 "2016-01-31T11:37:37Z")

</div>

Hi Peter, sorry for reviving this thread. For improvement of DX, wouldn’t it be possible that all cdt-list write ops automatically touch the bin / mark it as dirty? It’s quite counter-intuitive to lua beginners and can potentially cost developers hours to debug with the few examples available (none explaining the need for local bincopy = rec.binname).

With the new cdt list ops, it’s also unclear if that trick does a complete copy of the list instead of operating just on the elements changed (especially for in-memory namespace) - which would degrade performance a lot (though not a priority IMHO)! When benchmarking in-memory vs. ssd namespace (record udf using cdt list ops), I saw virtually no difference which I’d interpret as it’s actually doing a clone or the record lock starts throttling at 6000 record-udf apply’s/second.

Never saw the need for this with any other program using lua, too.

Cheers, Manuel