org.apache.pig.impl.logicalLayer.schema

Class Schema

java.lang.Object

org.apache.pig.impl.logicalLayer.schema.Schema

All Implemented Interfaces:

Serializable, Cloneable

public class Schema
extends Object
implements Serializable, Cloneable

The Schema class encapsulates the notion of a schema for a relational operator. A schema is a list of columns that describe the output of a relational operator. Each column in the relation is represented as a FieldSchema, a static class inside the Schema. A column by definition has an alias, a type and a possible schema (if the column is a bag or a tuple). In addition, each column in the schema has a unique auto generated name used for tracking the lineage of the column in a sequence of statements. The lineage of the column is tracked using a map of the predecessors' columns to the operators that generate the predecessor columns. The predecessor columns are the columns required in order to generate the column under consideration. Similarly, a reverse lookup of operators that generate the predecessor column to the predecessor column is maintained.

See Also:

Serialized Form

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	Schema.FieldSchema

Constructor Summary

Constructors

Constructor and Description
Schema()
Schema(List<Schema.FieldSchema> fields)
Schema(Schema.FieldSchema fieldSchema) Create a schema with only one field.
Schema(Schema s) Copy Constructor.

Method Summary

Modifier and Type	Method and Description
void	add(Schema.FieldSchema f)
void	addAlias(String alias, Schema.FieldSchema fs)
static boolean	castable(Schema cast, Schema input) Recursively compare two schemas to check if the input schema can be cast to the cast schema
Schema	clone() Make a deep copy of a schema.
boolean	equals(Object other) For two schemas to be equal, they have to be deeply equal.
static boolean	equals(Schema schema, Schema other, boolean relaxInner, boolean relaxAlias) Recursively compare two schemas for equality
Schema.FieldSchema	findFieldSchema(String canonicalName) Look for a FieldSchema instance in the schema hierarchy which has the given canonical name.
static Schema	generateNestedSchema(byte topLevelType, byte... innerTypes)
Set<String>	getAliases()
Schema.FieldSchema	getField(int fieldNum) Given a field number, find the associated FieldSchema.
Schema.FieldSchema	getField(String alias) Given an alias name, find the associated FieldSchema.
List<Schema.FieldSchema>	getFields()
Schema.FieldSchema	getFieldSubNameMatch(String alias) Given an alias name, find the associated FieldSchema.
static Schema	getPigSchema(ResourceSchema rSchema)
int	getPosition(String alias) Given an alias, find the associated position of the field schema.
int	getPositionSubName(String alias) Given an alias, find the associated position of the field schema.
int	hashCode()
boolean	isTwoLevelAccessRequired() Deprecated. twoLevelAccess is no longer needed
Schema	merge(Schema other, boolean otherTakesAliasPrecedence) Merge this schema with the other schema
Schema	mergePrefixSchema(Schema other, boolean otherTakesAliasPrecedence) Recursively prefix merge two schemas
Schema	mergePrefixSchema(Schema other, boolean otherTakesAliasPrecedence, boolean allowMergeableTypes) Recursively prefix merge two schemas
static Schema	mergeSchema(Schema schema, Schema other, boolean otherTakesAliasPrecedence) Recursively merge two schemas
static Schema	mergeSchema(Schema schema, Schema other, boolean otherTakesAliasPrecedence, boolean allowDifferentSizeMerge, boolean allowIncompatibleTypes) Recursively merge two schemas
static Schema	mergeSchemaByAlias(Schema schema1, Schema schema2) Merges two schemas using their column aliases (unlike mergeSchema(..) functions which merge using positions) Schema will not be merged if types are incompatible, as per DataType.mergeType(..) For Tuples and Bags, SubSchemas have to be equal be considered compatible
static Schema	mergeSchemasByAlias(Collection<Schema> schemas) Merges collection of schemas using their column aliases (unlike mergeSchema(..) functions which merge using positions) Schema will not be merged if types are incompatible, as per DataType.mergeType(..) For Tuples and Bags, SubSchemas have to be equal be considered compatible
String	prettyPrint()
void	printAliases()
void	reconcile(Schema other) Reconcile this schema with another schema.
static void	setSchemaDefaultType(Schema s, byte t) Recursively set NULL type to the specifid type in a schema
void	setTwoLevelAccessRequired(boolean twoLevelAccess) Deprecated. twoLevelAccess is no longer needed
int	size() Find the number of fields in the schema.
static void	stringifySchema(StringBuilder sb, Schema schema, byte type)
static void	stringifySchema(StringBuilder sb, Schema schema, byte type, int indentLevel)
String	toString()

Methods inherited from class java.lang.Object

finalize, getClass, notify, notifyAll, wait, wait, wait

Constructor Detail

Schema

public Schema()

Schema

public Schema(List<Schema.FieldSchema> fields)

Parameters:

fields - List of field schemas that describes the fields.

Schema

public Schema(Schema.FieldSchema fieldSchema)

Create a schema with only one field.

Parameters:

fieldSchema - field to put in this schema.

Schema

public Schema(Schema s)

Copy Constructor.

Parameters:

s - source schema

Method Detail

getField

public Schema.FieldSchema getField(String alias)
                            throws FrontendException

Given an alias name, find the associated FieldSchema.

Parameters:

alias - Alias to look up.

Returns:

FieldSchema, or null if no such alias is in this tuple.

Throws:

FrontendException

getFieldSubNameMatch

public Schema.FieldSchema getFieldSubNameMatch(String alias)
                                        throws FrontendException

Given an alias name, find the associated FieldSchema. If exact name is not found see if any field matches the part of the 'namespaced' alias. eg. if given alias is nm::a , and schema is (a,b). It will return FieldSchema of a. if given alias is nm::a and schema is (nm2::a, b), it will return null

Parameters:

alias - Alias to look up.

Returns:

FieldSchema, or null if no such alias is in this tuple.

Throws:

FrontendException

getField

public Schema.FieldSchema getField(int fieldNum)
                            throws FrontendException

Given a field number, find the associated FieldSchema.

Parameters:

fieldNum - Field number to look up.

Returns:

FieldSchema for this field.

Throws:

ParseException - if the field number exceeds the number of fields in the tuple.

FrontendException

size

public int size()

Find the number of fields in the schema.

Returns:

number of fields.

reconcile

public void reconcile(Schema other)
               throws FrontendException

Reconcile this schema with another schema. The schema being reconciled with should have the same number of columns. The use case is where a schema already exists but may not have alias and or type information. If an alias exists in this schema and a new one is given, then the new one will be used. Similarly with types, though this needs to be used carefully, as types should not be lightly changed.

Parameters:

other - Schema to reconcile with.

Throws:

ParseException - if this cannot be reconciled.

FrontendException

equals

public boolean equals(Object other)

For two schemas to be equal, they have to be deeply equal. Use Schema.equals(Schema schema, Schema other, boolean relaxInner, boolean relaxAlias) if relaxation of aliases is a requirement.

Overrides:

equals in class Object

clone

public Schema clone()
             throws CloneNotSupportedException

Make a deep copy of a schema.

Overrides:

clone in class Object

Throws:

CloneNotSupportedException

hashCode

public int hashCode()

Overrides:

hashCode in class Object

toString

public String toString()

Overrides:

toString in class Object

prettyPrint

public String prettyPrint()

stringifySchema

public static void stringifySchema(StringBuilder sb,
                                   Schema schema,
                                   byte type)
                            throws FrontendException

Throws:

FrontendException

stringifySchema

public static void stringifySchema(StringBuilder sb,
                                   Schema schema,
                                   byte type,
                                   int indentLevel)
                            throws FrontendException

Throws:

FrontendException

add

public void add(Schema.FieldSchema f)

getPosition

public int getPosition(String alias)
                throws FrontendException

Given an alias, find the associated position of the field schema.

Parameters:

alias - alias of the FieldSchema.

Returns:

position of the FieldSchema.

Throws:

FrontendException

getPositionSubName

public int getPositionSubName(String alias)
                       throws FrontendException

Given an alias, find the associated position of the field schema. It uses getFieldSubNameMatch to look for subName matches as well.

Parameters:

alias - alias of the FieldSchema.

Returns:

position of the FieldSchema.

Throws:

FrontendException

addAlias

public void addAlias(String alias,
                     Schema.FieldSchema fs)

getAliases

public Set<String> getAliases()

printAliases

public void printAliases()

getFields

public List<Schema.FieldSchema> getFields()

castable

public static boolean castable(Schema cast,
                               Schema input)

Recursively compare two schemas to check if the input schema can be cast to the cast schema

Parameters:

cast - schema of the cast operator

input - schema of the cast input

Returns:

true or falsew!

equals

public static boolean equals(Schema schema,
                             Schema other,
                             boolean relaxInner,
                             boolean relaxAlias)

Recursively compare two schemas for equality

Parameters:

schema -

other -

relaxInner - if true, inner schemas will not be checked

relaxAlias - if true, aliases will not be checked

Returns:

true if schemas are equal, false otherwise

merge

public Schema merge(Schema other,
                    boolean otherTakesAliasPrecedence)

Merge this schema with the other schema

Parameters:

other - the other schema to be merged with

otherTakesAliasPrecedence - true if aliases from the other schema take precedence

Returns:

the merged schema, null if they are not compatible

mergeSchema

public static Schema mergeSchema(Schema schema,
                                 Schema other,
                                 boolean otherTakesAliasPrecedence)

Recursively merge two schemas

Parameters:

schema - the initial schema

other - the other schema to be merged with

otherTakesAliasPrecedence - true if aliases from the other schema take precedence

Returns:

the merged schema, null if they are not compatible

mergeSchema

public static Schema mergeSchema(Schema schema,
                                 Schema other,
                                 boolean otherTakesAliasPrecedence,
                                 boolean allowDifferentSizeMerge,
                                 boolean allowIncompatibleTypes)
                          throws SchemaMergeException

Recursively merge two schemas

Parameters:

schema - the initial schema

other - the other schema to be merged with

otherTakesAliasPrecedence - true if aliases from the other schema take precedence

allowDifferentSizeMerge - allow merging of schemas of different types

allowIncompatibleTypes - 1) if types in schemas are not compatible they will be treated as ByteArray (untyped) 2) if schemas in schemas are not compatible and allowIncompatibleTypes is true those inner schemas in the output will be null.

Returns:

the merged schema this can be null if one schema is null and allowIncompatibleTypes is true

Throws:

SchemaMergeException - if they cannot be merged

mergeSchemasByAlias

public static Schema mergeSchemasByAlias(Collection<Schema> schemas)
                                  throws SchemaMergeException

Merges collection of schemas using their column aliases (unlike mergeSchema(..) functions which merge using positions) Schema will not be merged if types are incompatible, as per DataType.mergeType(..) For Tuples and Bags, SubSchemas have to be equal be considered compatible

Parameters:

schemas - - list of schemas to be merged using their column alias

Returns:

merged schema

Throws:

SchemaMergeException

mergeSchemaByAlias

public static Schema mergeSchemaByAlias(Schema schema1,
                                        Schema schema2)
                                 throws SchemaMergeException

Merges two schemas using their column aliases (unlike mergeSchema(..) functions which merge using positions) Schema will not be merged if types are incompatible, as per DataType.mergeType(..) For Tuples and Bags, SubSchemas have to be equal be considered compatible

Parameters:

schema1 -

schema2 -

Returns:

Merged Schema

Throws:

SchemaMergeException - if schemas cannot be merged

generateNestedSchema

public static Schema generateNestedSchema(byte topLevelType,
                                          byte... innerTypes)
                                   throws FrontendException

Parameters:

topLevelType - DataType type of the top level element

innerTypes - DataType types of the inner level element

Returns:

nested schema representing type of top level element at first level and inner schema representing types of inner element(s)

Throws:

FrontendException

mergePrefixSchema

public Schema mergePrefixSchema(Schema other,
                                boolean otherTakesAliasPrecedence)
                         throws SchemaMergeException

Recursively prefix merge two schemas

Parameters:

other - the other schema to be merged with

otherTakesAliasPrecedence - true if aliases from the other schema take precedence

Returns:

the prefix merged schema this can be null if one schema is null and allowIncompatibleTypes is true

Throws:

SchemaMergeException - if they cannot be merged

mergePrefixSchema

public Schema mergePrefixSchema(Schema other,
                                boolean otherTakesAliasPrecedence,
                                boolean allowMergeableTypes)
                         throws SchemaMergeException

Recursively prefix merge two schemas

Parameters:

other - the other schema to be merged with

otherTakesAliasPrecedence - true if aliases from the other schema take precedence

allowMergeableTypes - true if "mergeable" types should be allowed. Two types are mergeable if any of the following conditions is true IN THE BELOW ORDER of checks: 1) if either one has a type null or unknown and other has a type OTHER THAN null or unknown, the result type will be the latter non null/unknown type 2) If either type is bytearray, then result type will be the other (possibly non BYTEARRAY) type 3) If current type can be cast to the other type, then the result type will be the other type

Returns:

the prefix merged schema this can be null if one schema is null and allowIncompatibleTypes is true

Throws:

SchemaMergeException - if they cannot be merged

setSchemaDefaultType

public static void setSchemaDefaultType(Schema s,
                                        byte t)

Recursively set NULL type to the specifid type in a schema

Parameters:

s - the schema whose NULL type has to be set

t - the specified type

isTwoLevelAccessRequired

@Deprecated
public boolean isTwoLevelAccessRequired()

Deprecated. twoLevelAccess is no longer needed

Returns:

the twoLevelAccess

setTwoLevelAccessRequired

@Deprecated
public void setTwoLevelAccessRequired(boolean twoLevelAccess)

Deprecated. twoLevelAccess is no longer needed

Parameters:

twoLevelAccess - the twoLevelAccess to set

getPigSchema

public static Schema getPigSchema(ResourceSchema rSchema)
                           throws FrontendException

Throws:

FrontendException

findFieldSchema

public Schema.FieldSchema findFieldSchema(String canonicalName)

Look for a FieldSchema instance in the schema hierarchy which has the given canonical name.

Parameters:

canonicalName - canonical name

Returns:

the FieldSchema instance found