Property

• It represents a property of Model
• A Property has PropertType that represents the data type of that property.
• The Model class or Model instance provides methods such as .field() and .compute() to create Property instance.

There are two kinds of Property of a Model

Name	Description
FieldProperty	a field of a table.
ComputeProperty	a virtual field computed using other fields or SQL functions

FieldProperty

• It represents a field of a table and is defined in Model class.
• It can be created by method model.field() that accepts PropertyType constructor or PropertType instance. Please see PropertType for details.

Usage

Define various properties with different types and options.

Example:

export default class MyModel extends Model {
  // Nullable Integer
  prop1 = this.field(NumberType)

  // Nullable varchar(50)
  prop2 = this.field(new StringType({length: 50}))

  // Non-nullable varchar(255)
  prop3 = this.field(StringTypeNotNull)
}

In case, the field name can be overrided by a given name.

Example:

export default class MyModel extends Model {
  // the table field name would be 'p_r_o_p_1'
  prop1 = this.field(NumberType).setFieldName('p_r_o_p_1')
} 

Access Field Value using Datasource.$

Example:

// It selects records with prop1 equals 5
await MyModelRepo.find({
  where: ({root}) => root.prop1.equals(5)
})

ComputeProperty

• It represents a SQL value calculated by using other FieldProperty or SQL functions.
• It can be created by method Model.compute() that accepts a ComputeFunction.
• ComputeFunction that defines how to create a Scalar (a single SQL value). Please see PropertType for details.

ComputeFunction

• It is a function accepts two arguments
• returns a Scalar (a single SQL value)

Function Arguments	Descriptions	Optional
parent	Datasource of the current Model	No
arg	Value given in execution	Yes

A simple ComputeFunction Example:

(parent, args) => {
    // add 5 to the number value of prop1
    return parent.prop1.add(5)
})

CompiledComputeFunction

• It is a function that wraps the Datasource and call the ComputeFunction.
• Datasource.$ of a Model can access the CompiledComputeFunction of any Property of a Model
• Returns a Scalar (a single SQL value)

Function Arguments	Descriptions	Optional
arg	Value given in execution	Yes

Usage

Example 1:

Access the CompiledComputeFunction

class MyModel extends Model {
    prop1 = this.field(NumberType)
    prop2 = this.compute( 
      // add 5 to the number value of prop1
      (parent, arg) => parent.prop1.add(arg)
    )
}

const scalar = MyModel.datasource('alias1').$.prop2(5)

//Output SQL string: alias1.prop1 + 5
console.log(await scalar.toRaw() )

Example 2:

Use the CompiledComputeFunction in data query.

class MyModel extends Model {
    prop1 = this.field(NumberType)
    prop2 = this.compute( 
      // add 5 to the number value of prop1
      (parent, arg) => parent.prop1.add(arg)
    )
}

// It selects records with 
await MyModelRepo.find({
  where: ({root}) => root.prop2.equals(7))
})

The above codes, root is the Datasource.$. The find() method actually produce and execute the SQL:

SELECT root.prop1 
FROM MyModel AS root 
WHERE root.prop1 + 5 = 7