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## org.apache.cayenne.map
Class DerivedDbAttribute

    java.lang.Object
      org.apache.cayenne.map.Attribute
          org.apache.cayenne.map.DbAttribute
              org.apache.cayenne.map.DerivedDbAttribute

All Implemented Interfaces:
  java.io.Serializable, CayenneMapEntry, XMLSerializable

    public class DerivedDbAttribute

extends DbAttribute

A DerivedDbAttribute is a DbAttribute that resolves to an SQL expression based on a set of other attributes. DerivedDbAttribute's allow to build expressions like " `count(id)`", "`sum(price)`", etc.

Internally DerivedDbAttribute is defined as a specification string and a set of substitution DbAttribute parameters. Specification string is an SQL expression that contains placeholders (`%@`) for attribute parameters, for example:

`sum(%@) + sum(%@)`

Author:
  Andrei Adamchik
See Also:
  Serialized Form

Field Summary
`static java.lang.String` | `ATTRIBUTE_TOKEN`
`protected java.lang.String` | `expressionSpec`
`protected boolean` | `groupBy`
`protected java.util.List` | `params`

Fields inherited from class org.apache.cayenne.map.DbAttribute
`generated, mandatory, maxLength, precision, primaryKey, type`

Fields inherited from class org.apache.cayenne.map.Attribute
`entity, name`

Constructor Summary
`DerivedDbAttribute()` Constructor for DerivedDbAttribute.
`DerivedDbAttribute(DbEntity entity, DbAttribute parentProto)` Creates and initializes a derived attribute with an attribute of a parent entity.
`DerivedDbAttribute(java.lang.String name)` Constructor for DerivedDbAttribute.
`DerivedDbAttribute(java.lang.String name, int type, DbEntity entity, java.lang.String spec)` Constructor for DerivedDbAttribute.

Method Summary
`void` | `addParam(DbAttribute param)` Adds parameter.
`void` | `clearParams()`
`void` | `encodeAsXML(XMLEncoder encoder)` Prints itself as XML to the provided XMLEncoder.
`java.lang.String` | `getAliasedName(java.lang.String alias)`
`java.lang.String` | `getExpressionSpec()` Returns the expressionSpec.
`java.util.List` | `getParams()` Returns the params.
`boolean` | `isGroupBy()` Returns true if this attribute is used in GROUP BY clause of the parent entity.
`void` | `removeParam(DbAttribute param)`
`void` | `setExpressionSpec(java.lang.String expressionSpec)` Sets the expressionSpec.
`void` | `setGroupBy(boolean flag)`

Methods inherited from class org.apache.cayenne.map.DbAttribute
`getMaxLength, getPrecision, getType, isForeignKey, isGenerated, isMandatory, isPrimaryKey, setGenerated, setMandatory, setMaxLength, setPrecision, setPrimaryKey, setType`

Methods inherited from class org.apache.cayenne.map.Attribute
`getEntity, getName, getParent, setEntity, setName, setParent`

Methods inherited from class java.lang.Object
`clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

Field Detail

### ATTRIBUTE_TOKEN

    public static final java.lang.String ATTRIBUTE_TOKEN

See Also:
  Constant Field Values

### expressionSpec

    protected java.lang.String expressionSpec

### params

    protected java.util.List params

### groupBy

    protected boolean groupBy

Constructor Detail

### DerivedDbAttribute

    public DerivedDbAttribute()

  Constructor for DerivedDbAttribute.

### DerivedDbAttribute

    public DerivedDbAttribute(java.lang.String name)

  Constructor for DerivedDbAttribute.

### DerivedDbAttribute

    public DerivedDbAttribute(java.lang.String name,
                              int type,
                              DbEntity entity,
                              java.lang.String spec)

  Constructor for DerivedDbAttribute.

### DerivedDbAttribute

    public DerivedDbAttribute(DbEntity entity,
                              DbAttribute parentProto)

  Creates and initializes a derived attribute with an attribute of a parent entity.

Method Detail

### encodeAsXML

    public void encodeAsXML(XMLEncoder encoder)

  Prints itself as XML to the provided XMLEncoder.

  Specified by:
    `encodeAsXML` in interface `XMLSerializable`
  Overrides:
    `encodeAsXML` in class `DbAttribute`
  Since:
    1.1

### getAliasedName

    public java.lang.String getAliasedName(java.lang.String alias)

  Overrides:
    `getAliasedName` in class `DbAttribute`

### isGroupBy

    public boolean isGroupBy()

  Returns true if this attribute is used in GROUP BY clause of the parent entity.

### setGroupBy

    public void setGroupBy(boolean flag)

### getParams

    public java.util.List getParams()

  Returns the params.

  Returns:
    List

### getExpressionSpec

    public java.lang.String getExpressionSpec()

  Returns the expressionSpec.

### addParam

    public void addParam(DbAttribute param)

  Adds parameter.

### removeParam

    public void removeParam(DbAttribute param)

### clearParams

    public void clearParams()

### setExpressionSpec

    public void setExpressionSpec(java.lang.String expressionSpec)

  Sets the expressionSpec.

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