Counts the amount of entities in a table. If a filter is supplied, blinkDB will only count how many items match the filter - if not given, the total number of items in the table is returned.
// Get the total number of users
const userCount = await count(userTable);
// Get the number of users called Bob
const usersNamedBobCount = await count(userTable, {
where: {
name: "Bob",
},
});| Parameter | Description |
|---|---|
table
|
The table created by createTable() .
|
filter
| Optional. If given, only items matching the filter will be counted. See filters. |
| Option | Description |
|---|---|
exact (default: true)
| If the count should be exact, or estimated. See Performance. |
If no filter is given, count() will return in O(1) time.
If you specify a filter, BlinkDB will first retrieve all items, and then count how many items have been retrieved.
If you have a very large table (> 10.000 items), and prefer performance over accuracy, consider using { exact: false }. This
will use a more performant but less accurate method.
// Estimate the number of users called Bob
const usersNamedBobCount = await count(userTable, {
where: {
name: "Bob",
},
}, { exact: false });