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Document :pool_index #303

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merged 2 commits into from
Dec 2, 2023
Merged

Document :pool_index #303

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e88e7b5
document :pool_index
Dec 2, 2023
e115e14
wording
Dec 2, 2023
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27 changes: 24 additions & 3 deletions lib/db_connection.ex
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Expand Up @@ -389,9 +389,9 @@ defmodule DBConnection do
random exponential (default: `:rand_exp`)
* `:configure` - A function to run before every connect attempt to
dynamically configure the options, either a 1-arity fun,
`{module, function, args}` with options prepended to `args` or `nil` where
only returned options are passed to connect callback (default: `nil`). This
function is called *in the connection process*.
`{module, function, args}` or `nil`. This function is called
*in the connection process*. For more details, see
[Connection Configuration Callback](#start_link/2-connection-configuration-callback)
* `:after_connect` - A function to run on connect using `run/3`, either
a 1-arity fun, `{module, function, args}` with `t:DBConnection.t/0` prepended
to `args` or `nil` (default: `nil`)
Expand Down Expand Up @@ -524,6 +524,27 @@ defmodule DBConnection do
This feature is available since v2.6.0. Before this version `:connection_listeners` only
accepted a list of listener processes.

## Connection Configuration Callback

The `:configure` function will be called before each individual connection to the
database is made. It receives all of the options provided to `start_link/2` as well
as an additional generated value named `:pool_index`. The returned value will be
passed as the options into the appropriate `:connect` callback. This provides a way
for the user to dynamically configure the connection options.

`:pool_index` is an integer in `1..pool_size` that represents the current connection's
place in the enumeration of all of the pool's connections. It can be used, for example,
to configure a unique database per connection when asynchronous tests cannot be performed
on a single database.

The allowed callbacks are:

* A 1-arity function that recieves the options from `start_link/2` as well as
`:pool_index`
* `{module, function, args}` where the options from `start_link/2` as well as
`:pool_index` are prepended to `args` before the function is called
* `nil` if you do not want to modify the existing options

## Telemetry

A `[:db_connection, :connection_error]` event is published whenever a
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