aziz-w4-databases #45
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Week4/continentAggregation.js
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| $lookup: { | ||
| from: "continents", | ||
| localField: "_id", | ||
| foreignField: "Country", | ||
| as: "continent_info", |
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This is an cool way to get the continent info for each country, but it's more SQL-style as it would imply there's a continent collection that relations country and continent info.
Since the original data doesn't have a continents collection, could you find a way to get the population by contintent with only the original data? (Hint: Some of the documents have continents instead of countries for the Country field, e.g. "AFRICA", "OCEANIA". You need to find a way to filter for them)
| const fromAccountDoc = await accountsCollection.findOne({ | ||
| account_number: fromAccount, | ||
| }); | ||
| const toAccountDoc = await accountsCollection.findOne({ | ||
| account_number: toAccount, | ||
| }); |
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It's a good idea to include the session object inside the findOne documents. If they got modified outside the transaction mongodb will retry the transaction
Week4/transfer.js
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| $inc: { balance: -amount }, | ||
| $push: { | ||
| account_changes: { | ||
| change_number: Date.now(), |
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Using the current date and time is an interesting approach, but it doesn't accomplish the request in the instructions: "The change number should be incremented, so if the latest change_number is 30, the change_number for the new change should be 31."
How might you go about using an incrementing number here instead of a date?
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