Add support for mapping table and column name to different entity and field name

[daneshk]

Summary

The current bal persist design doesn't support mapping entities to the DB table that have different names. Always entity name and table name should be the same. The same thing applies to the column name and entity field name. When we do DB introspection, we need to support this.

[daneshk]

Proposed Design

# Defines the database column name which matches the record field. The default value is the record field name. 
public type MapConfig record {|
    # The DB table/column name
    string name;
|};

# The Annotation used to map database table and columns to record and record fields
public annotation MapConfig Map on record field, record;

So developer can give the mapping DB table name and column names for the record and record field using Mapping annotation in the data model definition as follows,

import ballerina/persist as _;
import ballerinax/persist.sql;

@sql:Map("DOCTORS")
type Doctor record {|
    @sql:Map("doc_id")
    readonly int id;
    string name;
    string specialty;
    string phoneNumber;
    Appointment[] appointment;
|};

[daneshk]

Based on the offline discussion, annotation names should be a noun instead of a verb.
@sameerajayasoma How about going with the @sql:Mapping annotation(Similar to @sql:Generated annotation) like the below?

import ballerina/persist as _;
import ballerinax/persist.sql;

@sql:Mapping("DOCTORS")
type Doctor record {|
    @sql:Mapping("doc_id")
    readonly int id;
    string name;
    string specialty;
    string phoneNumber;
    Appointment[] appointment;
|};

[daneshk]

Another option would be to have a Name annotation instead of a Mapping annotation similar to the xmldata module. like below,

# Defines the database column name which matches the record field. The default value is the record field name. 
public type NameConfig record {|
    # The DB table/column value
    string value;
|};

# The Annotation used to map database table and columns to record and record fields
public annotation NameConfig Name on record field, record;

The usages,

import ballerina/persist as _;
import ballerinax/persist.sql;

@sql:Name {value: "DOCTORS"}
type Doctor record {|
    @sql:Name {value: "doc_id"}
    readonly int id;
    string name;
    string specialty;
    string phoneNumber;
    Appointment[] appointment;
|};