Introduction

This document provides a rough analysis of what will be needed if the Ed-Fi ODS/API were to be converted over to run on another relational database management system (RDBMS). PostgreSQL was used as an anchor; however, many of the findings will be generally applicable to other RDBMS's.

placeholder for generalized analysis

PostgreSQL Conversion

An entire 2.5 ODS database was scripted out and paintstakingly converted over so that it would execute successfully as pg-sql, thus building out the full ODS schema in a postgres database.

Eliminate boilerplate at the top of the script - things related to SQL Cmd mode, connection properties (e.g. ansi_padding), etc.
Replace all [ ] qualifiers with nothing. Postgres uses quotation marks as qualifiers as needed. However, when you use them to create a object, then you are stuck permanently using them. Best to create without the quotation marks.
Create a dbo schema, belonging to the postgres user.
Alter other schemas so that they belong to the postgres user instead of dbo.

Fix data types

T-SQL Type	PG-SQL Type	Notes
NVARCHAR	VARCHAR	postgres implicitly converts unicode encodings on-the-fly. Since the Ed-Fi ODS is for use in the United States, UTF-16 support hardly seems necessary anyway.
DATETIME	TIMESTAMP	Not using TIMESTAMPTZ (with timezone) because the source data has no record of the time zone to begin with.
DATETIME2	TIMESTAMP
UNIQUEIDENTIFIER	CHAR(40)
BIT	SMALLINT	While postgres has a `bit` data type, it does not implicitly convert integer to bit. Instead it requires use a string '0' or '1' (or 'true', etc.). For maximum compatibility with existing code that uses the integer 0/1 instead of string '0'/'1', we should simply switch to `smallint`.

Postgres's cluster concept is different and more analysis is needed to know if it is needed (explicitly) for performance benefits. Remove CLUSTERED and NONCLUSTERED keywords from all indexes and primary key constraints. Also remove PAD_INDEX from constraints. Safe to leave in FILLFACTOR.
Remove WITH CHECK and NOCHECK from constraints.
The pg-equivalent of INT IDENTITY is SERIAL. Reg ex: /INT\s+IDENTITY\s*$1, 1$/ replace with SERIAL
Remove all PRINT statements and extended properties (table/column descriptions). Extended properties can be rewritten as COMMENTs but the effort was not worthwhile in this POC.

Views

Remove WITH SCHEMABINDING
Replace COUNT_BIG(*) with COUNT(*), as postgres's COUNT function already returns a big integer.
Remove all indexes on views.

In a real conversion, some views might need to materialized views for performance optimization.
Ensure that all view definitions end in a semi-colon.
In auth.LocalEducationAgencyIdToStaffUSI, cast null values as integer.

UNPIVOT must be rewritten with UNION ALL statements.

Click here to expand...

T-SQL

PG-SQL

CREATE VIEW [auth].[EducationOrganizationIdToStateAgencyId]
AS
    SELECT    DISTINCT StateEducationAgencyId, EdOrgId as EducationOrganizationId
    FROM
            (SELECT    * FROM auth.EducationOrganizationIdentifiers) As Source
    UNPIVOT (EdOrgId FOR IdType IN (EducationServiceCenterId, LocalEducationAgencyId, SchoolId)) -- Only ESCs, LEAs and Schools are accessible to State-level claims
            As UnpivotedSource
    UNION    
    -- State-level claims also can access the State
    SELECT    StateEducationAgencyId, StateEducationAgencyId AS EducationOrganizationId
    FROM    edfi.StateEducationAgency
GO

CREATE VIEW auth.EducationOrganizationIdToStateAgencyId
AS


    SELECT 
        StateEducationAgencyId,
        EducationServiceCenterId as EducationOrganizationId
    FROM
        auth.EducationOrganizationIdentifiers
    WHERE
        EducationServiceCenterId IS NOT NULL
    UNION
    SELECT 
        StateEducationAgencyId,
        LocalEducationAgencyId as EducationOrganizationId
    FROM
        auth.EducationOrganizationIdentifiers
    WHERE
        LocalEducationAgencyId IS NOT NULL
    UNION
    SELECT 
        StateEducationAgencyId,
        SchoolId as EducationOrganizationId
    FROM
        auth.EducationOrganizationIdentifiers
    WHERE
        SchoolId IS NOT NULL
    UNION   
    -- State-level claims also can access the State
    SELECT  StateEducationAgencyId, StateEducationAgencyId AS EducationOrganizationId
    FROM    edfi.StateEducationAgency;

Views that use common table expressions (CTE) recursively need to be modified by adding the keyword RECURSIVE immediately after WITH. Affected views: StudentAssessmentStudentObjectiveAssessmentH, ObjectiveAssessmentH_CTE, LocalEducationAgencyH, LearningStandardH, LearninbjectiveH, AssessmentFamilyH.
Default values in postgres are not constraints, so the syntax needs to be altered.
1. Substitute now() for getdate().
  From To
  /ALTER TABLE ([^\s]+)[\s\n]+(?:ADD CONSTRAINT (?:[^\s]+)) DEFAULT $getdate\($\) FOR (\w+)/ ALTER TABLE $1 ALTER COLUMN $2 SET DEFAULT now()
2. Replace newid() with uuid_generate_v4(). This requires first configuring uuid support by running CREATE EXTENSION "uuid-ossp".
  From To
  /ALTER TABLE ([^\s]+)[\s\n]+(?:ADD CONSTRAINT (?:[^\s]+)) DEFAULT $newid\($\) FOR (\w+)/ ALTER TABLE $1 ALTER COLUMN $2 SET DEFAULT uuid_generate_v4()

The maximum identifier length is 63. Longer identifiers are automatically truncated. This results in many foreign key names overlapping. To avoid this, use reasonable abbreviations to shorten these seven problematic beginnings to foreign keys:

From	To
fk_educationorganizationnetworkassociation_educationorganization	fk_edorgnetworkassociation_edorg
fk_learningstandardprerequisitelearningstandard_learningstandard	fk_lrnstdprerequisitelrnstd_lrnstd
fk_educationcontentderivativesourceeducationcontent_educationcontent	fk_edconderivativesourceedcon_edcon
fk_studentassessmentstudentobjectiveassessmentperformancelevel	fk_studassessmentstudobjassessmentperflvl
fk_postsecondaryeventpostsecondaryinstitutionidentificationcode	fk_pstscdryeventpstscdryinstidcode
fk_postsecondaryeventpostsecondaryinstitutionmediumofinstruction	fk_pstscdryeventpstscdryinstmediumofnstrn
fk_educationorganizationidentificationcode_educationorganization	fk_edorgidcode_edorg

Converting to PostgreSQL: Analysis

PostgreSQL Conversion