Sofiia-week4-databases #46
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| module.exports = { | ||
| getTotalPopulationByCountryAndYear, | ||
| getPopulationByContinentYearAndAge, | ||
| }; |
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It's very nice that you use modules. It really helps with the cleaner and readable code!
| $inc: { balance: -amount }, | ||
| $push: { | ||
| account_changes: { | ||
| change_number: fromAccount.account_changes.length + 1, |
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suggestion: using fromAccount.account_changes.length + 1 to know the next change_number is OK.
However, in real life one account may have a lot more change records. We don't really care what those changes are, we just want to know the maximum change number. Fetching all changes with the account can be expensive (since you need to transfer more bytes in the network. When you download something big from Internet, it is always slower than dowloading smaller files), and we try to only fetch the columns we need.
One solution is to have a function to get only the maximum change number (you have learned MAX sql syntax), and when you fetch the account data you don't fetch the changes column.
| change_number: toAccount.account_changes.length + 1, | ||
| amount: amount, |
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Same suggestion for max change number applies here too.
| if (!fromAccount || !toAccount) | ||
| throw new Error("One or both accounts not found."); | ||
| if (fromAccount.balance < amount) throw new Error("Insufficient funds."); |
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Early returns or throwing are always good things to do!
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Just notice you didn't close the client; remember to close the client after your code finish running! |
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