问题
I am trying to insert linked data in a pg-promise transaction. The transaction successfully inserts all the data correctly, but gives a warning UnhandledPromiseRejectionWarning: Error: Querying against a released or lost connection.
.
The code that causes this was originally:
const item = {
batch: { batch_number: 1 },
ingredients: [
{ amount: '12', unit: 'kg' },
{ amount: '4', unit: 'L' }
],
}
return await db.tx(async t => {
const batchQueryString = pgp.helpers.insert(item.batch, null, 'ionomer_batch')
const batchQuery = await t.one(batchQueryString + ' RETURNING ionomer_batch_id')
item.ingredients.forEach(async ingredient => {
const ingredientQueryString = pgp.helpers.insert(ingredient, null, 'ingredient')
const ingredientQuery = await t.one(ingredientQueryString + ' RETURNING ingredient_id')
await t.none(
`INSERT INTO ionomer_batch_step(ionomer_batch_id, ingredient_id)
VALUES(${batchQuery.ionomer_batch_id}, ${ingredientQuery.ingredient_id})`
)
})
return batchQuery
}).then(data => {
return {success: true, response: data}
}).catch(error => {
return {success: false, response: error}
})
I got it to work without producing a warning by doing
return await db.tx(async t => {
const batchQueryString = pgp.helpers.insert(item.batch, null, 'ionomer_batch')
const batchQuery = await t.one(batchQueryString + ' RETURNING ionomer_batch_id')
const ingredientQueries = []
// this can't be async
item.ingredients.forEach(ingredient => {
const ingredientQueryString = pgp.helpers.insert(ingredient, null, 'ingredient')
const ingredientQuery = t.one(ingredientQueryString + ' RETURNING ingredient_id')
ingredientQueries.push(ingredientQuery)
})
const resolvedIngredientQueries = await t.batch(ingredientQueries)
resolvedIngredientQueries.forEach(async ingredientQuery => {
await t.none(
`INSERT INTO ionomer_batch_step(ionomer_batch_id, ingredient_id)
VALUES(${batchQuery.ionomer_batch_id}, ${ingredientQuery.ingredient_id})`
)
})
return batchQuery
}).then(data => {
return {success: true, response: data}
}).catch(error => {
return {success: false, response: error}
})
but I now have to loop through twice instead of once, and I lose the async in the first loop. It seems like there should be a way to do something closer to the first attempt without hitting a warning about released or lost connections. I played around with chaining the queries, but couldn't get that to work.
回答1:
As an addition to @deanna own answer...
You do not really need to implement a loop. You can just re-map requests into array of promises, and then resolve it:
await db.tx(async t => {
const batchQueryString = pgp.helpers.insert(item.batch, null, 'ionomer_batch');
const batchQuery = await t.one(`${batchQueryString} RETURNING ionomer_batch_id`);
const inserts = item.ingredients.map(async i => {
const query = pgp.helpers.insert(i, null, 'ingredient');
const ingredientQuery = await t.one(`${query} RETURNING ingredient_id`);
return t.none(
`INSERT INTO ionomer_batch_step(ionomer_batch_id, ingredient_id)
VALUES($/batchQuery.ionomer_batch_id/, $/ingredientQuery.ingredient_id/)`,
{batchQuery, ingredientQuery});
});
await t.batch(inserts); // settle all generated promises
return batchQuery;
});
Also, you can see from the change, you should never use ES6 value injection like that. See here:
IMPORTANT: Never use the reserved
${}
syntax inside ES6 template strings, as those have no knowledge of how to format values for PostgreSQL. Inside ES6 template strings you should only use one of the 4 alternatives -$()
,$<>
,$[]
or$//
.
回答2:
As @vitaly-t said, I needed to ensure that the forEach loop actually completed.
A working solution is
const item = {
batch_number: 1,
},
ingredients: [
{ amount: '12', unit: 'kg' },
{ amount: '4', unit: 'L' }
],
}
return await db.tx(async t => {
const batchQueryString = pgp.helpers.insert(item.batch, null, 'ionomer_batch')
const batchQuery = await t.one(batchQueryString + ' RETURNING ionomer_batch_id')
await asyncForEach(item.ingredients, async ingredient => {
const ingredientQueryString = pgp.helpers.insert(ingredient, null, 'ingredient')
const ingredientQuery = await t.one(ingredientQueryString + ' RETURNING ingredient_id')
await t.none(
`INSERT INTO ionomer_batch_step(ionomer_batch_id, ingredient_id)
VALUES(${batchQuery.ionomer_batch_id}, ${ingredientQuery.ingredient_id})`
)
})
return batchQuery
}).then(data => {
return {success: true, response: data}
}).catch(error => {
return {success: false, response: error}
})
Where I had to make the helper function
async function asyncForEach(array, callback) {
for (let index = 0; index < array.length; index++) {
await callback(array[index], index, array);
}
}
as described here
来源:https://stackoverflow.com/questions/61805491/pg-promise-transaction-with-dependent-queries-in-foreach-loop-gives-warning-erro