Matlab map database objects

MATLAB Object Relational Mapper

Use when mapping MATLAB classes to relational database tables using the Object Relational Mapping (ORM) layer in Database Toolbox. Defines Mappable classes with property-to-column mappings and uses ormread, ormwrite, and ormupdate for CRUD operations on objects. Available since R2023b.

When to Use This Skill

• Mapping MATLAB classes to database tables
• Reading database rows as MATLAB objects
• Writing MATLAB objects to database tables
• Updating database rows from modified objects
• Generating SQL CREATE TABLE from a class definition
• Object-oriented database workflows
• User mentions keywords: ORM, object relational mapping, Mappable, ormread, ormwrite, ormupdate, orm2sql, class mapping, property mapping, object database

When NOT to Use

• Ad-hoc queries or data exploration — use sqlread/fetch with RowFilter instead
• Bulk imports/exports of thousands of rows — ORM is slower than sqlwrite/sqlread for bulk operations
• MongoDB, Cassandra, or Neo4j — ORM only works with relational databases (JDBC, ODBC, native MySQL/PostgreSQL/SQLite)
• MATLAB releases before R2023b — ORM is not available

Critical Rules

ORM Requirements

• ALWAYS inherit from database.orm.mixin.Mappable — this is required for ORM functionality.
• ALWAYS define at least one PrimaryKey property — ORM requires it for identity.
• ALWAYS use class-level attribute TableName to specify the database table name.
• ALWAYS include a constructor that handles nargin == 0 (allows preallocation by ORM).
• ORM requires R2023b or later.

Supported Connections

• ORM works with: JDBC, ODBC, PostgreSQL native, MySQL native, SQLite native, DuckDB native.
• ORM does NOT work with: MongoDB (mongoc), Cassandra (apacheCassandra), or Neo4j.

Decision Framework

Scenario	Use ORM	Use sqlread/sqlwrite
Object identity and business logic needed	Yes	No
Class-based type safety required	Yes	No
Domain validation on read/write	Yes	No
Ad-hoc queries or exploration	No	Yes
Bulk operations (thousands of rows)	No	Yes (faster)
No object mapping needed	No	Yes

Core Concepts

Defining a Mappable Class

A Mappable class maps MATLAB properties to database columns:

classdef (TableName = "employees") Employee < database.orm.mixin.Mappable

    properties (PrimaryKey, ColumnName = "EmployeeID")
        ID int32
    end

    properties
        Name string
        Department string
        Salary double
    end

    properties (ColumnName = "HireDate", ColumnType = "date")
        StartDate datetime
    end

    methods
        function obj = Employee(id, name, dept, salary, startDate)
            if nargin ~= 0
                obj.ID = id;
                obj.Name = name;
                obj.Department = dept;
                obj.Salary = salary;
                obj.StartDate = startDate;
            end
        end

        function obj = promote(obj, raise)
            obj.Salary = obj.Salary + raise;
        end
    end
end

Property Attributes Reference

Attribute	Purpose	Example
PrimaryKey	Marks property as the primary key (required)	properties (PrimaryKey)
ColumnName	Maps property to a differently-named column	properties (ColumnName = "EmpID")
ColumnType	Specifies the database column type	properties (ColumnType = "date")
TableName	Class-level attribute for the target table name	classdef (TableName = "employees")

Common Mistakes

% INCORRECT — class without PrimaryKey (ormwrite will error)
classdef (TableName = "employees") Employee < database.orm.mixin.Mappable
    properties
        Name string
        Dept string
    end
end
% ormwrite(conn, emp) → Error: No PrimaryKey defined

% CORRECT — PrimaryKey is required for ORM operations
classdef (TableName = "employees") Employee < database.orm.mixin.Mappable
    properties(PrimaryKey)
        EmployeeID int32
    end
    properties
        Name string
        Dept string
    end
end

% INCORRECT — class not inheriting Mappable
classdef Employee
    properties(PrimaryKey)
        EmployeeID int32
    end
end
% ormread(conn, "Employee") → Error! Not a Mappable class.

% CORRECT — must inherit from database.orm.mixin.Mappable
classdef Employee < database.orm.mixin.Mappable
    properties(PrimaryKey)
        EmployeeID int32
    end
end

% INCORRECT — constructor without nargin==0 guard
classdef (TableName = "emp") Employee < database.orm.mixin.Mappable
    methods
        function obj = Employee(id, name)
            obj.EmployeeID = id;
            obj.Name = name;
        end
    end
end
% ormread will fail because ORM needs to construct empty objects

% CORRECT — nargin==0 guard allows ORM to construct empty objects
classdef (TableName = "emp") Employee < database.orm.mixin.Mappable
    methods
        function obj = Employee(id, name)
            if nargin == 0
                return;
            end
            obj.EmployeeID = id;
            obj.Name = name;
        end
    end
end

Writing Objects with ormwrite

% Create and insert a single object
emp = Employee(1, "Alice", "Engineering", 95000, datetime(2023,3,15));
ormwrite(conn, emp);

% Create and insert an array of objects
emps = [Employee(2, "Bob", "Sales", 72000, datetime(2023,6,1)), ...
        Employee(3, "Carol", "Engineering", 105000, datetime(2022,1,10))];
ormwrite(conn, emps);

Reading Objects with ormread

% Read all objects
allEmployees = ormread(conn, "Employee");

% Read with a row filter
rf = rowfilter("Salary");
highEarners = ormread(conn, "Employee", RowFilter=rf.Salary > 90000);

% Refresh an existing object from database
emp = ormread(conn, emp);

Updating Objects with ormupdate

% Modify object in MATLAB
emp = promote(emp, 5000);

% Push changes to database
ormupdate(conn, emp);

Deleting Records

ORM does not provide an ormdelete function. Use execute for deletion:

execute(conn, "DELETE FROM employees WHERE EmployeeID = 42");

Error Handling

try
    ormwrite(conn, employeeObj);
catch ME
    if contains(ME.message, "UNIQUE") || contains(ME.message, "primary key")
        warning("Duplicate primary key. Use ormupdate instead.");
        ormupdate(conn, employeeObj);
    else
        rethrow(ME);
    end
end

Generating SQL from Class Definition

% View the CREATE TABLE SQL that corresponds to the class
sql = orm2sql(conn, "Employee");
disp(sql);
% Output: "CREATE TABLE employees (EmployeeID integer, Name text, ...)"

Complete Examples

Example 1: Full ORM Workflow — Define, Write, Read, Update

Step 1: Define the class (save as Product.m):

classdef (TableName = "products") Product < database.orm.mixin.Mappable

    properties (PrimaryKey, ColumnName = "ProductNumber")
        ID int32
    end

    properties
        Name string
        Description string
        Quantity int32
    end

    properties (ColumnName = "UnitCost")
        CostPerItem double
    end

    properties (ColumnType = "date")
        InventoryDate datetime
    end

    methods
        function obj = Product(id, name, desc, cost, qty, invDate)
            if nargin ~= 0
                obj.ID = id;
                obj.Name = name;
                obj.Description = desc;
                obj.CostPerItem = cost;
                obj.Quantity = qty;
                obj.InventoryDate = invDate;
            end
        end

        function obj = restock(obj, amount)
            obj.Quantity = obj.Quantity + amount;
            obj.InventoryDate = datetime("today");
        end
    end
end

Step 2: Use ORM operations (save as ormWorkflow.m):

(Uses the Product class defined above.)

% Connect to SQLite (no driver needed)
conn = sqlite("inventory.db", "create");

% Create and insert products
p1 = Product(1, "Widget", "Small widget", 9.99, 100, datetime(2024,1,1));
p2 = Product(2, "Gadget", "Large gadget", 29.99, 50, datetime(2024,1,1));
ormwrite(conn, [p1, p2]);

% Read all products back as objects
allProducts = ormread(conn, "Product");
disp(allProducts(1));

% Filter: find products under $15
rf = rowfilter("CostPerItem");
cheapProducts = ormread(conn, "Product", RowFilter=rf.CostPerItem < 15);

% Update: restock a product
cheapProducts(1) = restock(cheapProducts(1), 200);
ormupdate(conn, cheapProducts(1));

% Verify
refreshed = ormread(conn, cheapProducts(1));
disp(refreshed.Quantity); % Should be 300

close(conn);

Best Practices

• ALWAYS define Mappable classes in their own .m file — one class per file (MATLAB requirement).
• ALWAYS include a constructor that handles nargin == 0 (allows preallocation).
• ALWAYS mark exactly one property block with PrimaryKey.
• Use ColumnName when the MATLAB property name differs from the database column name.
• Use ColumnType for types that need explicit mapping (e.g., "date" for datetime).
• Use ormread with RowFilter to import only the objects you need — pushes filter to database.
• Use orm2sql to verify your class mapping matches the expected database schema before writing.
• Modify objects in MATLAB using class methods, then push changes with ormupdate.

Common Patterns

Pattern 1: Define-Write-Read-Update

% Define class → Product.m
p = Product(1, "Item", "Desc", 9.99, 10, datetime("today"));
ormwrite(conn, p);
p = ormread(conn, p);        % Refresh from DB
p = restock(p, 50);          % Modify in MATLAB
ormupdate(conn, p);          % Push to DB

Pattern 2: Filtered Read with Business Logic

rf = rowfilter("Quantity");
lowStock = ormread(conn, "Product", RowFilter=rf.Quantity < 10);
for i = 1:numel(lowStock)
    lowStock(i) = restock(lowStock(i), 100);
    ormupdate(conn, lowStock(i));
end

Pattern 3: Schema Verification

sql = orm2sql(conn, "MyClass");
disp(sql); % Verify CREATE TABLE matches expectations

Checklist

Before finalizing, verify:

• Mappable class inherits from database.orm.mixin.Mappable
• Class has TableName attribute on classdef
• At least one property block has PrimaryKey attribute
• Constructor handles nargin == 0 for preallocation
• Class saved in its own .m file
• Connection established and verified (isopen(conn))
• Connection type is supported (JDBC, ODBC, MySQL/PostgreSQL/SQLite/DuckDB native)
• R2023b or later (ORM not available in earlier releases)

Troubleshooting

Issue: ormwrite fails with "class is not Mappable"

• Solution: Ensure the class inherits from database.orm.mixin.Mappable. The class definition must include < database.orm.mixin.Mappable.

Issue: ormread returns empty array

• Solution: Verify the table exists in the database using sqlfind(conn, tableName). Verify the class TableName attribute matches the actual table name.

Issue: ormupdate doesn't change database values

• Solution: ormupdate matches rows by primary key. Verify the object's primary key property value exists in the database. Use ormread to refresh and check.

Issue: Property-to-column mapping is incorrect

• Solution: Use orm2sql(conn, "ClassName") to inspect the generated SQL. Verify ColumnName and ColumnType attributes match the database schema.

Issue: ORM functions not found ("Undefined function")

• Solution: ORM requires R2023b or later. Check your release with ver('database'). For older releases, use sqlread/sqlwrite instead.

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