View Source Ecto.Adapters.Tds (Ecto SQL v3.9.1)
Adapter module for MSSQL Server using the TDS protocol.
Tds options split in different categories described below. All options can be given via the repository configuration.
:hostname- Server hostname
:port- Server port (default: 1433)
:password- User password
:database- the database to connect to
:pool- The connection pool module, may be set to
:ssl- Set to true if ssl should be used (default: false)
:ssl_opts- A list of ssl options, see Erlang's
:show_sensitive_data_on_connection_error- show connection data and configuration whenever there is an error attempting to connect to the database
We also recommend developers to consult the
for a complete list of all supported options for driver.
:collation- the database collation. Used during database creation but it is ignored later
If you need collation other than Latin1, add
tds_encoding as dependency to
mix.exs file then amend
config/config.ex by adding:
config :tds, :text_encoder, Tds.Encoding
This should give you extended set of most encoding. For complete list check
After connect flags
After connecting to MSSQL server, TDS will check if there are any flags set in connection options that should affect connection session behaviour. All flags are MSSQL standard SET options. The following flags are currently supported:
:set_language- sets session language (consult stored procedure output
exec sp_helplanguagefor valid values)
:set_datefirst- number in range 1..7
:set_dateformat- atom, one of
:mdy | :dmy | :ymd | :ydm | :myd | :dym
:set_deadlock_priority- atom, one of
:low | :high | :normal | -10..10
:set_lock_timeout- number in milliseconds > 0
:set_remote_proc_transactions- atom, one of
:on | :off
:set_implicit_transactions- atom, one of
:on | :off
:set_allow_snapshot_isolation- atom, one of
:on | :off(required if
Repo.transaction(fn -> ... end, isolation_level: :snapshot)is used)
:set_read_committed_snapshot- atom, one of
:on | :off
MSSQL server has slightly different binary storage format for UUIDs (
If you use
:binary_id, the proper choice is made. Otherwise you must use the
type. Avoid using
Ecto.UUID since it may cause unpredictable application behaviour.
When working with binaries and strings,there are some limitations you should be aware of:
Strings that should be stored in mentioned sql types must be encoded to column codepage (defined in collation). If collation is different than database collation, it is not possible to store correct value into database since the connection respects the database collation. Ecto does not provide way to override parameter codepage.
If you need other than Latin1 or other than your database default collation, as mentioned in "Storage Options" section, then manually encode strings using
Tds.Encoding.encode/2into desired codepage and then tag parameter as
:binary. Please be aware that queries that use this approach in where clauses can be 10x slower due increased logical reads in database.
You can't store VarChar codepoints encoded in one collation/codepage to column that is encoded in different collation/codepage. You will always get wrong result. This is not adapter or driver limitation but rather how string encoding works for single byte encoded strings in MSSQL server. Don't be confused if you are always seeing latin1 chars, they are simply in each codepoint table.
In particular, if a field has the type
:text, only raw binaries will be allowed.
To avoid above limitations always use
:string (NVarChar) type for text if possible.
If you really need to use VarChar's column type, you can use the
Even though the adapter will convert
:map fields into JSON back and forth,
actual value is stored in NVarChar column.
Query hints and table hints
MSSQL supports both query hints and table hints: https://docs.microsoft.com/en-us/sql/t-sql/queries/hints-transact-sql-query
For Ecto compatibility, the query hints must be given via the
lock option, and they
will be translated to MSSQL's "OPTION". If you need to pass multiple options, you
can separate them by comma:
from query, lock: "HASH GROUP, FAST 10"
Table hints are specified as a list alongside a
from query, hints: ["INDEX (IX_Employee_ManagerID)"]
:migration_lock will be treated as a table hint and defaults to "UPDLOCK".
Multi Repo calls in transactions
To avoid deadlocks in your app, we exposed
:isolation_level repo transaction option.
This will tell to SQL Server Transaction Manager how to begin transaction.
By default, if this option is omitted, isolation level is set to
Any attempt to manually set the transaction isolation via queries, such as
Ecto.Adapter.SQL.query("SET TRANSACTION ISOLATION LEVEL XYZ")
will fail once explicit transaction is started using
and reset back to :read_committed.
Ecto.Query.lock/3 function can help by setting it to
This should allow you to do eventually consistent reads and avoid locks on given
table if you don't need to write to database.
NOTE: after explicit transaction ends (commit or rollback) implicit transactions will run as READ_COMMITTED.