Projection (Flink : Table : Common 1.19.1 API)

java.lang.Object
- org.apache.flink.table.connector.Projection

```
@PublicEvolving
public abstract class Projection
extends Object
```
Projection represents a list of (possibly nested) indexes that can be used to project data types. A row projection includes both reducing the accessible fields and reordering them.

Method Summary

All Methods Static Methods Instance Methods Abstract Methods Concrete Methods
Modifier and Type	Method and Description
`static Projection`	`all(DataType dataType)` Create a `Projection` of all the fields in the provided `dataType`.
`Projection`	`complement(DataType dataType)` Like `complement(int)`, using the `dataType` fields count.
`abstract Projection`	`complement(int fieldsNumber)` Complement this projection.
`abstract Projection`	`difference(Projection other)` Perform a difference of this `Projection` with another `Projection`.
`static Projection`	`empty()` Create an empty `Projection`, that is a projection that projects no fields, returning an empty `DataType`.
`boolean`	`equals(Object o)`
`static Projection`	`fromFieldNames(DataType dataType, List<String> projectedFields)` Create a `Projection` of the provided `dataType` using the provided `projectedFields`.
`int`	`hashCode()`
`abstract boolean`	`isNested()`
`static Projection`	`of(int[] indexes)` Create a `Projection` of the provided `indexes`.
`static Projection`	`of(int[][] indexes)` Create a `Projection` of the provided `indexes`.
`abstract DataType`	`project(DataType dataType)` Projects a (possibly nested) row data type by returning a new data type that only includes fields of the given index paths.
`LogicalType`	`project(LogicalType logicalType)` Same as `project(DataType)`, but accepting and returning `LogicalType`.
`static Projection`	`range(int startInclusive, int endExclusive)` Create a `Projection` of a field range.
`abstract int[][]`	`toNestedIndexes()` Convert this instance to a nested projection index paths.
`String`	`toString()`
`abstract int[]`	`toTopLevelIndexes()` Convert this instance to a projection of top level indexes.

Methods inherited from class java.lang.Object
clone, finalize, getClass, notify, notifyAll, wait, wait, wait

- Method Detail
  - project
```
public abstract DataType project(DataType dataType)
```
    Projects a (possibly nested) row data type by returning a new data type that only includes fields of the given index paths.
    When extracting nested fields, the name of the resulting fields is the full path of the field separated by _. For example, the field b inside the row field a of the root DataType is named a_b in the result DataType. In case of naming conflicts the postfix notation '_$%d' is used, where %d is an arbitrary number, in order to generate a unique field name. For example if the root DataType includes both a field a_b and a nested row a with field b, the result DataType will contain one field named a_b and the other named a_b_1.
  - project
```
public LogicalType project(LogicalType logicalType)
```
    Same as project(DataType), but accepting and returning LogicalType.
  - isNested
```
public abstract boolean isNested()
```
    Returns:
    
    true whether this projection is nested or not.
  - difference
```
public abstract Projection difference(Projection other)
```
    Perform a difference of this Projection with another Projection. The result of this operation is a new Projection retaining the same ordering of this instance but with the indexes from other removed. For example:
```
 
 [4, 1, 0, 3, 2] - [4, 2] = [1, 0, 2]
 
 
```
    Note how the index 3 in the minuend becomes 2 because it's rescaled to project correctly a RowData or arity 3.
    Parameters:
    
    other - the subtrahend
    
    Throws:
    
    IllegalArgumentException - when other is nested.
  - complement
```
public abstract Projection complement(int fieldsNumber)
```
    Complement this projection. The returned projection is an ordered projection of fields from 0 to fieldsNumber except the indexes in this Projection. For example:
```
 
 [4, 2].complement(5) = [0, 1, 3]
 
 
```
    Parameters:
    
    fieldsNumber - the size of the universe
    
    Throws:
    
    IllegalStateException - if this projection is nested.
  - complement
```
public Projection complement(DataType dataType)
```
    Like complement(int), using the dataType fields count.
  - toTopLevelIndexes
```
public abstract int[] toTopLevelIndexes()
```
    Convert this instance to a projection of top level indexes. The array represents the mapping of the fields of the original DataType. For example, [0, 2, 1] specifies to include in the following order the 1st field, the 3rd field and the 2nd field of the row.
    
    Throws:
    
    IllegalStateException - if this projection is nested.
  - toNestedIndexes
```
public abstract int[][] toNestedIndexes()
```
    Convert this instance to a nested projection index paths. The array represents the mapping of the fields of the original DataType, including nested rows. For example, [[0, 2, 1], ...] specifies to include the 2nd field of the 3rd field of the 1st field in the top-level row.
  - empty
```
public static Projection empty()
```
    Create an empty Projection, that is a projection that projects no fields, returning an empty DataType.
  - of
```
public static Projection of(int[] indexes)
```
    Create a Projection of the provided indexes.
    
    See Also:
    
    toTopLevelIndexes()
  - of
```
public static Projection of(int[][] indexes)
```
    Create a Projection of the provided indexes.
    
    See Also:
    
    toNestedIndexes()
  - fromFieldNames
```
public static Projection fromFieldNames(DataType dataType,
                                        List<String> projectedFields)
```
    Create a Projection of the provided dataType using the provided projectedFields.
  - all
```
public static Projection all(DataType dataType)
```
    Create a Projection of all the fields in the provided dataType.
  - range
```
public static Projection range(int startInclusive,
                               int endExclusive)
```
    Create a Projection of a field range.
  - equals
```
public boolean equals(Object o)
```
    Overrides:
    
    equals in class Object
  - hashCode
```
public int hashCode()
```
    Overrides:
    
    hashCode in class Object
  - toString
```
public String toString()
```
    Overrides:
    
    toString in class Object

Class Projection

Method Summary

Methods inherited from class java.lang.Object

Method Detail

project

project

isNested

difference

complement

complement

toTopLevelIndexes

toNestedIndexes

empty

of

of

fromFieldNames

all

range

equals

hashCode

toString