Converting "NULL" to a Null value

[cisaacson]

We have are creating a Vec<String> for params, and then passing them to params_from_iter on the vec and overall it works great. It coerces the type to the proper type in the database based on the type hint (such as REAL) when used in a prepared statement for a REPLACE INTO. These statements have a fixed number of parameter values. We are currently generating the params in the Vec dynamically. We now have a use case to make some of the parameters Null values, and obviously a string of "NULL" will not work since that is an actual value, not a Null value. Given that the Vec must contain homogeneous values, is there an easy way to do this?

I am not sure how we would use this with the params_from_iter. The params_from_iter takes a Vec<String> so it doesn't seem like the right solution.

We use params_from_iter because it made it easy to pass the right number of params, but perhaps we need to do it another way (like the params! macro with a fixed number of params). There are many different types of statements which we store and execute later, using the dynamic number of params required for that statement. using the params! macro it does not seem possible to do this.

We could easily make an enum with data, a String and Null type value in 2 variants, and create a Vec of those. But then how would we pass those to each prepared statement, when various statements have various numbers of params?

Any suggestions appreciated.

Great product by the way, really easy to use and very fast.

[trevyn]

I think using Option just works for this.

[cisaacson]

Thanks @trevyn. So that means we could just use a Vec<Option<String>> as the argument to params_from_iter and it would work? I suppose it would coerce a None to a Null type and Some to the proper value for the type needed for the prepared statement. If so that makes things very easy. I will try it.

[thomcc]

Yes. You should also be able to use an iterator that yields those, if you don't want to build the Vec in memory.

[cisaacson]

Perfect, thanks for the quick help. I will close the discussion topic.