Struct datafusion::execution::context::SessionContext

pub struct SessionContext { /* private fields */ }

SessionContext is the main interface for executing queries with DataFusion. It stands for the connection between user and DataFusion/Ballista cluster. The context provides the following functionality

• Create DataFrame from a CSV or Parquet data source.
• Register a CSV or Parquet data source as a table that can be referenced from a SQL query.
• Register a custom data source that can be referenced from a SQL query.
• Execution a SQL query

The following example demonstrates how to use the context to execute a query against a CSV data source using the DataFrame API:

use datafusion::prelude::*;
let ctx = SessionContext::new();
let df = ctx.read_csv("tests/data/example.csv", CsvReadOptions::new()).await?;
let df = df.filter(col("a").lt_eq(col("b")))?
           .aggregate(vec![col("a")], vec![min(col("b"))])?
           .limit(0, Some(100))?;
let results = df.collect();

The following example demonstrates how to execute the same query using SQL:

use datafusion::prelude::*;

let mut ctx = SessionContext::new();
ctx.register_csv("example", "tests/data/example.csv", CsvReadOptions::new()).await?;
let results = ctx.sql("SELECT a, MIN(b) FROM example GROUP BY a LIMIT 100").await?;

Implementations

impl SessionContext

pub fn new() -> Self

Creates a new execution context using a default session configuration.

pub async fn refresh_catalogs(&self) -> Result<()>

Finds any ListSchemaProviders and instructs them to reload tables from “disk”

pub fn with_config(config: SessionConfig) -> Self

Creates a new session context using the provided session configuration.

pub fn with_config_rt(config: SessionConfig, runtime: Arc<RuntimeEnv>) -> Self

Creates a new session context using the provided configuration and RuntimeEnv.

pub fn with_state(state: SessionState) -> Self

Creates a new session context using the provided session state.

pub fn session_start_time(&self) -> DateTime<Utc>

Returns the time this session was created

pub fn register_batch(
    &self,
    table_name: &str,
    batch: RecordBatch
) -> Result<Option<Arc<dyn TableProvider>>>

Registers the [RecordBatch] as the specified table name

pub fn runtime_env(&self) -> Arc<RuntimeEnv>

Return the RuntimeEnv used to run queries with this SessionContext

pub fn session_id(&self) -> String

Return the session_id of this Session

pub fn copied_config(&self) -> SessionConfig

Return a copied version of config for this Session

pub async fn sql(&self, sql: &str) -> Result<DataFrame>

Creates a DataFrame that will execute a SQL query.

Note: This api implements DDL such as CREATE TABLE and CREATE VIEW with in memory default implementations.

If this is not desirable, consider using SessionState::create_logical_plan() which does not mutate the state based on such statements.

pub fn register_variable(
    &self,
    variable_type: VarType,
    provider: Arc<dyn VarProvider + Send + Sync>
)

Registers a variable provider within this context.

pub fn register_udf(&self, f: ScalarUDF)

Registers a scalar UDF within this context.

Note in SQL queries, function names are looked up using lowercase unless the query uses quotes. For example,

SELECT MY_FUNC(x)... will look for a function named "my_func" SELECT "my_FUNC"(x) will look for a function named "my_FUNC"

pub fn register_udaf(&self, f: AggregateUDF)

Registers an aggregate UDF within this context.

Note in SQL queries, aggregate names are looked up using lowercase unless the query uses quotes. For example,

SELECT MY_UDAF(x)... will look for an aggregate named "my_udaf" SELECT "my_UDAF"(x) will look for an aggregate named "my_UDAF"

pub async fn read_avro(
    &self,
    table_path: impl AsRef<str>,
    options: AvroReadOptions<'_>
) -> Result<DataFrame>

Creates a DataFrame for reading an Avro data source.

pub async fn read_json(
    &self,
    table_path: impl AsRef<str>,
    options: NdJsonReadOptions<'_>
) -> Result<DataFrame>

Creates a DataFrame for reading an Json data source.

pub fn read_empty(&self) -> Result<DataFrame>

Creates an empty DataFrame.

pub async fn read_csv(
    &self,
    table_path: impl AsRef<str>,
    options: CsvReadOptions<'_>
) -> Result<DataFrame>

Creates a DataFrame for reading a CSV data source.

pub async fn read_parquet(
    &self,
    table_path: impl AsRef<str>,
    options: ParquetReadOptions<'_>
) -> Result<DataFrame>

Creates a DataFrame for reading a Parquet data source.

pub fn read_table(&self, provider: Arc<dyn TableProvider>) -> Result<DataFrame>

Creates a DataFrame for reading a custom TableProvider.

pub fn read_batch(&self, batch: RecordBatch) -> Result<DataFrame>

Creates a DataFrame for reading a [RecordBatch]

pub async fn register_listing_table(
    &self,
    name: &str,
    table_path: impl AsRef<str>,
    options: ListingOptions,
    provided_schema: Option<SchemaRef>,
    sql_definition: Option<String>
) -> Result<()>

Registers a [ListingTable] that can assemble multiple files from locations in an ObjectStore instance into a single table.

This method is async because it might need to resolve the schema.

pub async fn register_csv(
    &self,
    name: &str,
    table_path: &str,
    options: CsvReadOptions<'_>
) -> Result<()>

Registers a CSV file as a table which can referenced from SQL statements executed against this context.

pub async fn register_json(
    &self,
    name: &str,
    table_path: &str,
    options: NdJsonReadOptions<'_>
) -> Result<()>

Registers a Json file as a table that it can be referenced from SQL statements executed against this context.

pub async fn register_parquet(
    &self,
    name: &str,
    table_path: &str,
    options: ParquetReadOptions<'_>
) -> Result<()>

Registers a Parquet file as a table that can be referenced from SQL statements executed against this context.

pub async fn register_avro(
    &self,
    name: &str,
    table_path: &str,
    options: AvroReadOptions<'_>
) -> Result<()>

Registers an Avro file as a table that can be referenced from SQL statements executed against this context.

pub fn register_catalog(
    &self,
    name: impl Into<String>,
    catalog: Arc<dyn CatalogProvider>
) -> Option<Arc<dyn CatalogProvider>>

Registers a named catalog using a custom CatalogProvider so that it can be referenced from SQL statements executed against this context.

Returns the CatalogProvider previously registered for this name, if any

pub fn catalog_names(&self) -> Vec<String>

Retrieves the list of available catalog names.

pub fn catalog(&self, name: &str) -> Option<Arc<dyn CatalogProvider>>

Retrieves a CatalogProvider instance by name

pub fn register_table<'a>(
    &'a self,
    table_ref: impl Into<TableReference<'a>>,
    provider: Arc<dyn TableProvider>
) -> Result<Option<Arc<dyn TableProvider>>>

Registers a TableProvider as a table that can be referenced from SQL statements executed against this context.

Returns the TableProvider previously registered for this reference, if any

pub fn deregister_table<'a>(
    &'a self,
    table_ref: impl Into<TableReference<'a>>
) -> Result<Option<Arc<dyn TableProvider>>>

Deregisters the given table.

Returns the registered provider, if any

pub fn table_exist<'a>(
    &'a self,
    table_ref: impl Into<TableReference<'a>>
) -> Result<bool>

Return true if the specified table exists in the schema provider.

pub async fn table<'a>(
    &self,
    table_ref: impl Into<TableReference<'a>>
) -> Result<DataFrame>

Retrieves a DataFrame representing a table previously registered by calling the register_table function.

Returns an error if no table has been registered with the provided reference.

pub async fn table_provider<'a>(
    &self,
    table_ref: impl Into<TableReference<'a>>
) -> Result<Arc<dyn TableProvider>>

Return a TableProvider for the specified table.

pub fn tables(&self) -> Result<HashSet<String>>

👎Deprecated: Please use the catalog provider interface (SessionContext::catalog) to examine available catalogs, schemas, and tables

Returns the set of available tables in the default catalog and schema.

Use table to get a specific table.

pub fn optimize(&self, plan: &LogicalPlan) -> Result<LogicalPlan>

👎Deprecated: Use SessionState::optimize to ensure a consistent state for planning and execution

Optimizes the logical plan by applying optimizer rules.

pub async fn create_physical_plan(
    &self,
    logical_plan: &LogicalPlan
) -> Result<Arc<dyn ExecutionPlan>>

👎Deprecated: Use SessionState::create_physical_plan or DataFrame::create_physical_plan to ensure a consistent state for planning and execution

Creates a physical plan from a logical plan.

pub async fn write_csv(
    &self,
    plan: Arc<dyn ExecutionPlan>,
    path: impl AsRef<str>
) -> Result<()>

Executes a query and writes the results to a partitioned CSV file.

pub async fn write_json(
    &self,
    plan: Arc<dyn ExecutionPlan>,
    path: impl AsRef<str>
) -> Result<()>

Executes a query and writes the results to a partitioned JSON file.

pub async fn write_parquet(
    &self,
    plan: Arc<dyn ExecutionPlan>,
    path: impl AsRef<str>,
    writer_properties: Option<WriterProperties>
) -> Result<()>

Executes a query and writes the results to a partitioned Parquet file.

pub fn task_ctx(&self) -> Arc<TaskContext>

Get a new TaskContext to run in this session

pub fn state(&self) -> SessionState

Snapshots the SessionState of this SessionContext setting the query_execution_start_time to the current time

pub fn state_weak_ref(&self) -> Weak<RwLock<SessionState>>

Get weak reference to SessionState

pub fn register_catalog_list(&mut self, catalog_list: Arc<dyn CatalogList>)

Register CatalogList in SessionState

Trait Implementations

impl Clone for SessionContext

fn clone(&self) -> SessionContext

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Default for SessionContext

fn default() -> Self

Returns the “default value” for a type.

impl From<&SessionContext> for TaskContext

Create a new task context instance from SessionContext

fn from(session: &SessionContext) -> Self

Converts to this type from the input type.

impl FunctionRegistry for SessionContext

fn udfs(&self) -> HashSet<String>

Set of all available udfs.

fn udf(&self, name: &str) -> Result<Arc<ScalarUDF>>

Returns a reference to the udf named name.

fn udaf(&self, name: &str) -> Result<Arc<AggregateUDF>>

Returns a reference to the udaf named name.