org.apache.calcite.schema

Interface Schema

All Known Subinterfaces:

SchemaPlus, SemiMutableSchema

All Known Implementing Classes:

AbstractSchema, CloneSchema, DelegatingSchema, JdbcSchema, ReflectiveSchema

public interface Schema

A namespace for tables and functions.

A schema can also contain sub-schemas, to any level of nesting. Most providers have a limited number of levels; for example, most JDBC databases have either one level ("schemas") or two levels ("database" and "catalog").

There may be multiple overloaded functions with the same name but different numbers or types of parameters. For this reason, getFunctions(java.lang.String) returns a list of all members with the same name. Calcite will call Schemas.resolve(org.apache.calcite.rel.type.RelDataTypeFactory, String, java.util.Collection, java.util.List) to choose the appropriate one.

The most common and important type of member is the one with no arguments and a result type that is a collection of records. This is called a relation. It is equivalent to a table in a relational database.

For example, the query

select * from sales.emps

is valid if "sales" is a registered schema and "emps" is a member with zero parameters and a result type of Collection(Record(int: "empno", String: "name")).

A schema may be nested within another schema; see getSubSchema(String).

Nested Class Summary

Nested Classes

Modifier and Type	Interface and Description
static class	Schema.TableType Table type.

Method Summary

Methods

Modifier and Type	Method and Description
boolean	contentsHaveChangedSince(long lastCheck, long now) Returns whether the contents of this schema have changed since a given time.
Expression	getExpression(SchemaPlus parentSchema, String name) Returns the expression by which this schema can be referenced in generated code.
Set<String>	getFunctionNames() Returns the names of the functions in this schema.
Collection<Function>	getFunctions(String name) Returns a list of functions in this schema with the given name, or an empty list if there is no such function.
Schema	getSubSchema(String name) Returns a sub-schema with a given name, or null.
Set<String>	getSubSchemaNames() Returns the names of this schema's child schemas.
Table	getTable(String name) Returns a table with a given name, or null if not found.
Set<String>	getTableNames() Returns the names of the tables in this schema.
boolean	isMutable() Returns whether the user is allowed to create new tables, functions and sub-schemas in this schema, in addition to those returned automatically by methods such as getTable(String).

Method Detail

getTable

Table getTable(String name)

Returns a table with a given name, or null if not found.

Parameters:

name - Table name

Returns:

Table, or null

getTableNames

Set<String> getTableNames()

Returns the names of the tables in this schema.

Returns:

Names of the tables in this schema

getFunctions

Collection<Function> getFunctions(String name)

Returns a list of functions in this schema with the given name, or an empty list if there is no such function.

Parameters:

name - Name of function

Returns:

List of functions with given name, or empty list

getFunctionNames

Set<String> getFunctionNames()

Returns the names of the functions in this schema.

Returns:

Names of the functions in this schema

getSubSchema

Schema getSubSchema(String name)

Returns a sub-schema with a given name, or null.

Parameters:

name - Sub-schema name

Returns:

Sub-schema with a given name, or null

getSubSchemaNames

Set<String> getSubSchemaNames()

Returns the names of this schema's child schemas.

Returns:

Names of this schema's child schemas

getExpression

Expression getExpression(SchemaPlus parentSchema,
                       String name)

Returns the expression by which this schema can be referenced in generated code.

Parameters:

parentSchema - Parent schema

name - Name of this schema

Returns:

Expression by which this schema can be referenced in generated code

isMutable

boolean isMutable()

Returns whether the user is allowed to create new tables, functions and sub-schemas in this schema, in addition to those returned automatically by methods such as getTable(String).

Even if this method returns true, the maps are not modified. Calcite stores the defined objects in a wrapper object.

Returns:

Whether the user is allowed to create new tables, functions and sub-schemas in this schema

contentsHaveChangedSince

boolean contentsHaveChangedSince(long lastCheck,
                               long now)

Returns whether the contents of this schema have changed since a given time. The time is a millisecond value, as returned by System.currentTimeMillis(). If this method returns true, and caching is enabled, Calcite will re-build caches.

The default implementation in AbstractSchema always returns false.

To control whether Calcite caches the contents of a schema, use the "cache" JSON attribute. The default value is "true".

Parameters:

lastCheck - The last time that Calcite called this method, or Long.MIN_VALUE if this is the first call

now - The current time in millis, as returned by System.currentTimeMillis()

Returns:

Whether contents changed after lastCheckMillis.