New Features¶ ↑

A Sequel.split_symbols setting has been added. This setting is true by default, so there is no change to backwards compatibility by default. However, users can now do:
```
Sequel.split_symbols = false
```
to disable the splitting of symbols. This will make Sequel no longer treat symbols with double or triple underscores as qualified or aliased identifiers, instead treating them as plain identifiers. It will also make Sequel no longer treat virtual row methods with double underscores as qualified identifiers. Examples:
```
# Sequel.split_symbols = true
:column                    # "column"
:table__column             # "table"."column"
:column___alias            # "column" AS "alias"
:table__column___alias     # "table"."column" AS "alias"
Sequel.expr{table__column} # "table"."column"

# Sequel.split_symbols = false
:column                    # "column"
:table__column             # "table__column"
:column___alias            # "column___alias"
:table__column___alias     # "table__column___alias"
Sequel.expr{table__column} # "table__column"
```
Disabling symbol splitting can make things much easier if leading trailing, double, or triple underscores are used in identifiers in your database.

Disabling symbol splitting makes Sequel simpler, even if it does make it slightly less easy to create qualified and aliased identifiers. It is possible that the symbol splitting will be disabled by default starting in Sequel 5.

Note that due to Database symbol literal caching, you should not change the Sequel.split_symbols setting after creating a Database instance.
SQL::Identifier#[] and SQL::QualifiedIdentifier#[] have been added for creating qualified identifiers. This makes it easier and more natural to create qualified identifiers from existing identifiers. Previously, you could do:
```
Sequel[:column].qualify(:table)
```
You can now use the more natural:
```
Sequel[:table][:column]
```
This can also be used in virtual rows:
```
Sequel.expr{table[:column]}
```
This offers a easy way to create qualified identifers when symbol splitting has been disabled.
A symbol_aref extension has been added, allowing the use of Symbol#[] to create qualified identifiers if passed a Symbol, SQL::Identifier, or SQL::QualifiedIdentifier. This doesn’t break any existing ruby behavior, as ruby currrently raises an exception in such cases. Example:
```
:table[:column] # "table"."column"
```
This extension can make it easier to create qualified identifiers if symbol splitting is disabled.

A symbol_aref_refinement extension has also been added, which adds a refinement version of the extension that can be enabled via:
```
using Sequel::SymbolAref
```
A symbol_as extension has been added, which adds the Symbol#as method to create aliased identifiers. This was previously part of the core extensions, but has been separated so it can be included by itself. Example:
```
:column.as(:alias) # "column" AS "alias"
```
This extension can make it easier to create aliased identifiers if symbol splitting is disabled.

A symbol_as_refinement extension has also been added, which adds a refinement version of the extension that can be enabled via:
```
using Sequel::SymbolAs
```
An s extension has been added, which adds the Sequel::S module, containing a private S method that calls Sequel.expr. You can include this module in any module or class where you would like the S method to be available:
```
class Album < Sequel::Model
  extend Sequel::S
  one_to_many :tracks, :order=>S(:number).desc
end
```
You can include this in Object if you want the S method to be available globally:
```
Object.send(:include, Sequel::S)
```
Sequel::S also works if it is used as a refinement, adding the S method to Object while the refinement is active:
```
using Sequel::S
```
This extension can make it easier to create qualified and aliased identifiers if symbol splitting is disabled:
```
S(:table)[:column]
S(:column).as(:alias)
```

Dataset#insert_conflict on PostgreSQL now supports a :conflict_where option, allowing for the handling of insert conflicts when using a partial unique index:

DB[:table].insert_conflict(:target=>:a,
  :conflict_where=>{:c=>true}).insert(:a=>1, :b=>2)
# INSERT INTO TABLE (a, b) VALUES (1, 2)
# ON CONFLICT (a) WHERE (c IS TRUE) DO NOTHING

Other Improvements¶ ↑

Sequel no longer attempts to combine arguments for non-associative operators, as doing so leads to invalid code in cases such as:
```
Sequel.expr{column1 - (column2 - 1)}
```
Sequel now automatically adds NOT NULL constraints on columns when adding a primary key constraint on the columns, if the database doesn’t handle that situation correctly.
Database#rollback_checker now returns a thread-safe object.
SQL::QualifiedIdentifier#initialize now converts SQL::Identifier arguments to strings, fixing usage of such objects in the schema methods.
The prepared_statements plugin now correctly handles lookup by primary key on models with joined datasets.
The dataset_associations plugin now handles many_through_many and one_through_many associations that use a single join table. Note there is no reason to create such associations, as many_to_many and one_through_one associations will work for such cases.
The insert_returning_select plugin now handles cases where the model doesn’t have a valid dataset, fixing usage with the lazy_attributes and dataset_associations plugins, and potentially other plugins.
The column_select plugin no longer raises an exception if the model’s table does not exist.
The class_table_inheritance plugin now works when the prepared_statements plugin is also used.
Some adapters now avoid thread-safety issues during loading on ruby implementations without a GVL by avoiding the modification of shared datastructures.
When using Database#tables with the :qualify=>true option on PostgreSQL, table names with double or triple underscores are now handled correctly.

Backwards Compatibility¶ ↑

The following Dataset constants are now frozen: NON_SQL_OPTIONS, ACTION_METHODS, QUERY_METHODS, CONDITIONED_JOIN_TYPES, UNCONDITIONED_JOIN_TYPES, and JOIN_METHODS. Of these, NON_SQL_OPTIONS was previously modified in a non-thread-safe manner by some adapters. External adapters should switch to having the adapter’s dataset non_sql_options method return an array of options that do not affect the SELECT SQL for the adapter’s datasets, rather than modifying NON_SQL_OPTIONS.

4.40.0.txt

New Features¶ ↑

Other Improvements¶ ↑

Backwards Compatibility¶ ↑