Documentation for custom rendering strategies

Author: jeffgbutler

CHANGELOG.md

@@ -9,6 +9,7 @@ GitHub milestone: [https://github.com/mybatis/mybatis-dynamic-sql/issues?q=miles
 ### Added
 
 - Added a general insert statement that does not require a separate record class to hold values for the insert. ([#201](https://github.com/mybatis/mybatis-dynamic-sql/issues/201))
+- Added the capability to specify a rendering strategy on a column to override the defaut rendering strategy for a statement. This will allow certain edge cases where a parameter marker needs to be formatted in a unique way (for example, "::jsonb" needs to be added to parameter markers for JSON fields in PostgreSQL) ([#200](https://github.com/mybatis/mybatis-dynamic-sql/issues/200))
 
 ## Release 1.1.4 - November 23, 2019
 

src/site/markdown/docs/databaseObjects.md

@@ -130,14 +130,18 @@ Whenever the table is referenced for rendering SQL, the name will be calculated
 
 ## Column Representation
 
-The class `org.mybatis.dynamic.sql.SqlColumn` is used to represent a column in a table or view. An `SqlColumn` is always associated with a `SqlTable`. In it's most basic form, the `SqlColumn` class holds a name and a reference to the `SqlTable` it is associated with.
+The class `org.mybatis.dynamic.sql.SqlColumn` is used to represent a column in a table or view. An `SqlColumn` is always associated with a `SqlTable`. In it's most basic form, the `SqlColumn` class holds a name and a reference to the `SqlTable` it is associated with. The table reference is required so that table aliases can be applied to columns in the rendering phase.
+
+The `SqlColumn` will be rendered in SQL based on the `RenderingStrategy` applied to the SQL statement. Typically the rendering strategy generates a string that represents a parameter marker in whatever SQL engine you are using. For example, MyBatis3 parameter markers are formatted as "#{some_attribute}". By default all columns are rendered with the same strategy. The library supplies rendering strategies that are appropriate for several SQL execution engines including MyBatis3 and Spring JDBC template.
+
+In some cases it is necessary to override the rendering strategy for a particular column - so the `SqlColumn` class supports specifying a rendering strategy for a column that will override the rendering strategy applied to a statement. A good example of this use case is with PostgreSQL. In that database it is required to add the string "::jsonb" to a prepared statement parameter marker when inserting or updating JSON fields, but not for other fields. A column based rendering strategy enables this.
 
 The `SqlColumn` class has additional optional attributes that are useful for SQL rendering - especially in MyBatis3. These include:
 
 * The `java.sql.JDBCType` of the column. This will be rendered into the MyBatis3 compatible parameter marker - which helps with picking type handlers and also inserting or updating null capable fields
 * A String containing a type handler - either a type handler alias or the fully qualified type of a type handler. This will be rendered into the MyBatis3 compatible parameter marker
 
-If you are not using MyBatis3, then you will not need to specify the JDBC Type or type handler.
+If you are not using MyBatis3, then you will not need to specify the JDBC Type or type handler as those attributes are ignored by other rendering strategies.
 
 Finally, the `SqlColumn` class has methods to designate a column alias or sort order for use in different SQL statements.