Check if a struct is empty

Asked Jan 17 '19 at 11:59

Active Jan 17 '19 at 11:59

Viewed 4,670 times

I have a function where I pass a id. With that id the contract find in a mapping a struct. My idea is to check if exists that struct with the given id with a if clause.

I try with 0, null, "".

Is that possible? Thx

asked Jan 17 '19 at 11:59

UnexpectedCharacter

3

Add a bool valid field to your struct, set it to true whenever you add a struct to the mapping, and use it in order to check whether or not the struct is valid (i.e., whether or not it "exists"). – goodvibration Jan 17 '19 at 12:04
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Like @goodvibration said, add a field to your struct, that you set when the record is created, then you can use that to check if it was initialised or not. Mappings that are not "initialised" will always return null / 0 / "" if data was not saved to said slot, so you need to check based on variables that actually change the state when saved. – Micky Socaci Jan 17 '19 at 12:39
Thx for the support ;D – UnexpectedCharacter Jan 17 '19 at 12:51
Have you seen this? https://ethereum.stackexchange.com/questions/13167/are-there-well-solved-and-simple-storage-patterns-for-solidity – Rob Hitchens Jan 17 '19 at 17:31
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Possible duplicate of Are there well-solved and simple storage patterns for Solidity? – Briomkez Jan 20 '19 at 21:45
My solution like this; When delete struct with delete keyword, zeros all struct values. You can check not expected any key stored as 0 value. You know, when add new key to your struct, it increase gas fee. – Fatih Mert Doğancan Mar 22 '22 at 22:05

Check if a struct is empty

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