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

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

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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