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📖 Table of Contents

1. ER2CDS Model
2. Entity
3. Attributes
4. Relationship

ER2CDS Model

ER2CDS models are specified in .er2cds files with the er2cds keyword and a model name. After the header follows the specification of the model elements (i.e. entities and relationships).

Entity

An entity includes a name and an optional alias, as well as attributes within curly braces.

// Entity with Alias
entity withAlias {
   alias Alias
}

// Entity with Attributes
entity withAttributes {
   key attr1 : CHAR
   attr2 : CHAR
}

Attributes

// Classifiers
attr
key attr
no-out attr

// Datatype
attr : CHAR

// Alias
attr : CHAR as Attribute

Classifiers

Classifier	Description
none	Simple
key	Key attributes
no-out	Used for modeling; not part of CDS output

Datatypes

Datatype	Description
DEC	Calculation/amount field
INT1	Single-byte integer
INT2	Two-byte integer
INT4	Four-byte integer
CURR	Currency field
CUKY	Currency key
QUAN	Quantity
UNIT	Unit
FLTP	Floating point number
NUMC	Numeric text
CHAR	Character
LCHR	Long Character
STRG	String of variable length
RSTR	Byte string of variable length
DATS	Date
ACCP	Accounting period YYYYMM
TIMS	Time HHMMSS
RAW	Byte string
LRAW	Long byte string
CLNT	Client
LANG	Language
D16D	Decimal Floating Point Stored as Binary Number
D16R	Decimal Floating Point Stored as Binary Number
D34D	Decimal Floating Point Stored in BCD Format
D34R	Decimal Floating Point Stored as Binary Number
INT8	8-Byte Integer
PREC	Two-byte integer
SSTR	Character String

Relationship

Degree

We require all relationships to be binary.

relationship Binary {
    E1 -> E2
}

Type

ER2CDS supports all types of CDS relationships. For explanation please refer to the official documentation.

// Join relationship
relationship Join {
}

// Association relationship
association relationship Association {
}

// Association-to-Parent relationship
association-to-parent relationship Association-to-Parent {
}

// Composition relationship
composition relationship Composition {
}

Cardinality

Cardinality corresponds to the maximum constraint in the number of allowed entity instances. The value for cardinality can be either 1 (one) or 0..N (many).

// 1-1 (One-To-One)
relationship Rel1 {
    E1[1] -> E2[1]
}

// 1-N (One-To-Many)
relationship Rel2 {
    E1[1] -> E2[0..N]
}

// N-N (Many-To-Many)
relationship Rel3 {
    E1[0..N] -> E2[0..N]
}

Join Order

The join order determines the order of joins in the resulting CDS view entity.

// Join gets executed first
relationship Rel1 {
    E1[1] -> E2[1]
    join order 1
}

// Join gets executed second
relationship Rel2 {
    E1[1] -> E2[0..N]
    join order 2
}

Join Clauses

The join clauses are interpreted as the ON clause within a join.

// Join with defined on-clause
relationship Rel1 {
    E1[1] -> E2[1]
    join order 1
    attr11 = attr21
    attr12 = attr22
}