sap-abap-cds

What this skill does

# SAP ABAP CDS (Core Data Services)

## Related Skills

- **sap-abap**: Use for ABAP programming patterns used with CDS or when implementing EML statements in ABAP
- **sap-btp-cloud-platform**: Use for CDS deployment scenarios on BTP or ABAP Environment configurations
- **sap-fiori-tools**: Use when building Fiori Elements applications that consume CDS views or working with UI annotations
- **sap-cap-capire**: Use for comparing CDS syntax between ABAP and CAP or when integrating ABAP CDS with CAP services
- **sap-api-style**: Use when documenting CDS-based OData services or following API documentation standards

**Quick Reference**: [https://help.sap.com/doc/abapdocu_cp_index_htm/CLOUD/en-US/abencds.html](https://help.sap.com/doc/abapdocu_cp_index_htm/CLOUD/en-US/abencds.html) | SAP Cheat Sheets: [https://github.com/SAP-samples/abap-cheat-sheets/blob/main/15_CDS_View_Entities.md](https://github.com/SAP-samples/abap-cheat-sheets/blob/main/15_CDS_View_Entities.md)

## Version Compatibility

This skill covers CDS features from **7.40 SP8** through **ABAP Cloud**. Key version boundaries:

| Feature | 7.40 SP8 | 7.50 | 7.51 | 7.55+ |
|---------|:--------:|:----:|:----:|:-----:|
| CDS View (`DEFINE VIEW`) | x | x | x | x |
| CDS associations, parameters, built-in functions | x | x | x | x |
| CDS Table Functions (`DEFINE TABLE FUNCTION`) | | x | x | x |
| CDS Access Control (DEFINE ROLE / pfcg_auth) | x | x | x | x |
| CDS Access Control (implicit evaluation) | | x | x | x |
| Session variables (`$session.user/client/system_language`) | x | x | x | x |
| `@Environment.systemField` annotation | | x | x | x |
| `UPPER`/`LOWER` functions | | | x | x |
| `$session.system_date` | | | x | x |
| CDS Metadata Extensions (`ANNOTATE VIEW`) | | | x | x |
| Cross Join in CDS | | | x | x |
| **CDS View Entity (`DEFINE VIEW ENTITY`)** | | | | x |
| New cardinality syntax (`to one`/`to many`) | | | | 7.57+ |

**On a 7.40 system**: Use `DEFINE VIEW` (not `DEFINE VIEW ENTITY`). CDS table functions
are **not available** before 7.50. Basic DCL (`DEFINE ROLE` with `pfcg_auth`) is available
from 7.40 SP08, but implicit role evaluation in ABAP SQL requires 7.50+.
`$session.user/client/system_language` are available from 7.40 SP08.
The templates in `templates/` include both classic CDS View and View Entity variants.

## Table of Contents
- [1. CDS View Fundamentals](#1-cds-view-fundamentals)
- [2. Essential Annotations](#2-essential-annotations)
- [3. Expressions and Operations](#3-expressions-and-operations)
- [4. Built-in Functions](#4-built-in-functions)
- [5. Joins](#5-joins)
- [6. Associations](#6-associations)
- [7. Input Parameters](#7-input-parameters)
- [8. Aggregate Expressions](#8-aggregate-expressions)
- [9. Access Control (DCL)](#9-access-control-dcl)
- [10. Data Retrieval from ABAP](#10-data-retrieval-from-abap)
- [11. Common Errors and Solutions](#11-common-errors-and-solutions)
- [12. Useful Transactions and Tables](#12-useful-transactions-and-tables)
- [Bundled Resources](#bundled-resources)
- [Source Documentation](#source-documentation)

---

## 1. CDS View Fundamentals

### View Types

| Type | Syntax | Database View | Since |
|------|--------|---------------|-------|
| **CDS View** | `DEFINE VIEW` | Yes | 7.4 SP8 |
| **CDS View Entity** | `DEFINE VIEW ENTITY` | No | 7.55 |

**Recommendation**: Use CDS View Entities for new development.

### Basic CDS View Syntax

```sql
@AbapCatalog.sqlViewName: 'ZCDS_EXAMPLE_V'
@AbapCatalog.compiler.CompareFilter: true
@AccessControl.authorizationCheck: #NOT_REQUIRED
@EndUserText.label: 'Example CDS View'

define view ZCDS_EXAMPLE
  as select from db_table as t
{
  key t.field1,
      t.field2,
      t.field3 as AliasName
}
```

### CDS View Entity Syntax (7.55+)

```sql
@AccessControl.authorizationCheck: #NOT_REQUIRED
@EndUserText.label: 'Example View Entity'

define view entity Z_CDS_EXAMPLE
  as select from db_table as t
{
  key t.field1,
      t.field2,
      t.field3 as AliasName
}
```

**Key Difference**: View entities omit `@AbapCatalog.sqlViewName` - no SQL view generated.

### Eclipse ADT Setup
1. **File** → **New** → **Other** → **Core Data Services** → **Data Definition**
2. Enter name, description, and package
3. Select template (view, view entity, etc.)

---

## 2. Essential Annotations

### Core Annotations

**Essential annotations for CDS development**:
- `@AbapCatalog.sqlViewName` - SQL view name (max 16 chars)
- `@AbapCatalog.compiler.CompareFilter` - Optimize WHERE clauses
- `@AccessControl.authorizationCheck` - Set to #NOT_REQUIRED, #CHECK, #MANDATORY, or #NOT_ALLOWED
- `@EndUserText.label` - User-facing description
- `@Metadata.allowExtensions` - Allow view extensions

**Complete Reference**: See `references/annotations-reference.md` for 50+ annotations with examples.

### Semantics Annotations (Currency/Quantity)

**Required for CURR and QUAN data types** to avoid error SD_CDS_ENTITY105:

```sql
-- Currency fields
@Semantics.currencyCode: true
waers,
@Semantics.amount.currencyCode: 'waers'
amount,

-- Quantity fields
@Semantics.unitOfMeasure: true
meins,
@Semantics.quantity.unitOfMeasure: 'meins'
quantity
```

### UI Annotations (Fiori Elements)

```sql
@UI.lineItem: [{ position: 10 }]
@UI.identification: [{ position: 10 }]
@UI.selectionField: [{ position: 10 }]
field1,

@UI.hidden: true
internal_field
```

### Consumption Annotations (Value Help)

```sql
@Consumption.valueHelpDefinition: [{
  entity: { name: 'I_Currency', element: 'Currency' }
}]
waers
```

For complete annotation reference, see `references/annotations-reference.md`.

---

## 3. Expressions and Operations

### CASE Expressions

**Simple CASE** (single variable comparison):
```sql
case status
  when 'A' then 'Active'
  when 'I' then 'Inactive'
  else 'Unknown'
end as StatusText
```

**Searched CASE** (multiple conditions):
```sql
case
  when amount > 1000 then 'High'
  when amount > 100 then 'Medium'
  else 'Low'
end as AmountCategory
```

### Comparison Operators

**Standard operators**: `=`, `<>`, `<`, `>`, `<=`, `>=`
**Special operators**: `BETWEEN x AND y`, `LIKE`, `IS NULL`, `IS NOT NULL`

**Complete Reference**: See `references/expressions-reference.md` for all operators and expressions.

### Arithmetic Operations

```sql
quantity * price as TotalAmount,
amount / 100 as Percentage,
-amount as NegatedAmount
```

### Session Variables

**Available system variables** (SY fields equivalent):
- `$session.user` (SY-UNAME) - Current user **[7.40 SP08+]**
- `$session.client` (SY-MANDT) - Client **[7.40 SP08+]**
- `$session.system_language` (SY-LANGU) - Language **[7.40 SP08+]**
- `$session.system_date` (SY-DATUM) - Current date **[7.51+]**

> **Note**: `$session.user/client/system_language` are available from 7.40 SP08.
> `$session.system_date` requires 7.51+. `@Environment.systemField` requires 7.50+.

**Complete Reference**: See `references/expressions-reference.md` for all system variables.

```sql
$session.user as CurrentUser,
$session.system_date as Today
```

---

## 4. Built-in Functions

CDS provides comprehensive built-in functions for string, numeric, and date operations.

### Key Function Categories
- **String Functions**: concat(), length(), substring(), upper(), lower(), replace()
- **Numeric Functions**: abs(), ceil(), floor(), round(), division()
- **Date Functions**: dats_add_days(), dats_add_months(), dats_days_between()
- **CAST Expression**: Convert between ABAP data types

> **Note**: `upper()` and `lower()` in CDS require **7.51+**. On 7.40/7.50, case
> conversion must be performed in ABAP after selecting (there is no CDS equivalent).

**Complete Reference**: See `references/functions-reference.md` for all 50+ functions with examples.

### Quick Examples
```sql
-- String operations
concat(first_name, last_name) as FullName,
upper(name) as UpperName,
substring(description, 1, 10) as ShortDesc

-- Numeric operations  
abs(amount) as AbsoluteAmount,
round(value, 2) as RoundedValue,
division(10, 3, 2) as PreciseDivisio