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dbt Classes

dbt has a number of classes it uses to represent objects in a data warehouse, parts of a dbt project, and the results of a command.

These classes are often useful when building advanced dbt models and macros.

Relation​

The Relation object is used to interpolate schema and table names into SQL code with appropriate quoting. This object should always be used instead of interpolating values with {{ schema }}.{{ table }} directly. Quoting of the Relation object can be configured using the quoting config.

Creating relations​

A Relation can be created by calling the create class method on the Relation class.

Relation.create
class Relation:
  def create(database=None, schema=None, identifier=None,
             type=None):
  """
    database (optional): The name of the database for this relation
    schema (optional): The name of the schema (or dataset, if on BigQuery) for this relation
    identifier (optional): The name of the identifier for this relation
    type (optional): Metadata about this relation, eg: "table", "view", "cte"
  """

Using relations​

In addition to api.Relation.create, dbt returns a Relation when you use ref, source or this.

relation_usage.sql
{% set relation = api.Relation.create(schema='snowplow', identifier='events') %}

-- Return the `database` for this relation
{{ relation.database }}

-- Return the `schema` (or dataset) for this relation
{{ relation.schema }}

-- Return the `identifier` for this relation
{{ relation.identifier }}

-- Return relation name without the database
{{ relation.include(database=false) }}

-- Return true if the relation is a table
{{ relation.is_table }}

-- Return true if the relation is a view
{{ relation.is_view }}

-- Return true if the relation is a cte
{{ relation.is_cte }}

Column​

The Column object is used to encode information about a column in a relation.

column.py
class Column(object):
  def __init__(self, column, dtype, char_size=None, numeric_size=None):
    """
      column: The name of the column represented by this object
      dtype: The data type of the column (database-specific)
      char_size: If dtype is a variable width character type, the size of the column, or else None
      numeric_size: If dtype is a fixed precision numeric type, the size of the column, or else None
   """


# Example usage:
col = Column('name', 'varchar', 255)
col.is_string() # True
col.is_numeric() # False
col.is_number() # False
col.is_integer() # False
col.is_float() # False
col.string_type() # character varying(255)
col.numeric_type('numeric', 12, 4) # numeric(12,4)

Column API​

Properties​

  • name: Returns the name of the column
  • quoted: Returns the name of the column wrapped in quotes
  • data_type: Returns the data type of the column

Instance methods​

  • is_string(): Returns True if the column is a String type (eg. text, varchar), else False
  • is_numeric(): Returns True if the column is a fixed-precision Numeric type (eg. numeric), else False
  • is_number(): Returns True if the column is a number-y type (eg. numeric, int, float, or similar), else False
  • is_integer(): Returns True if the column is an integer (eg. int, bigint, serial or similar), else False
  • is_float(): Returns True if the column is a float type (eg. float, float64, or similar), else False
  • string_size(): Returns the width of the column if it is a string type, else, an exception is raised

Static methods​

  • string_type(size): Returns a database-useable representation of the string type (eg. character varying(255))
  • numeric_type(dtype, precision, scale): Returns a database-useable representation of the numeric type (eg. numeric(12, 4))

Using columns​

column_usage.sql
-- String column
{%- set string_column = api.Column('name', 'varchar', char_size=255) %}

-- Return true if the column is a string
{{ string_column.is_string() }}

-- Return true if the column is a numeric
{{ string_column.is_numeric() }}

-- Return true if the column is a number
{{ string_column.is_number() }}

-- Return true if the column is an integer
{{ string_column.is_integer() }}

-- Return true if the column is a float
{{ string_column.is_float() }}

-- Numeric column
{%- set numeric_column = api.Column('distance_traveled', 'numeric', numeric_precision=12, numeric_scale=4) %}

-- Return true if the column is a string
{{ numeric_column.is_string() }}

-- Return true if the column is a numeric
{{ numeric_column.is_numeric() }}

-- Return true if the column is a number
{{ numeric_column.is_number() }}

-- Return true if the column is an integer
{{ numeric_column.is_integer() }}

-- Return true if the column is a float
{{ numeric_column.is_float() }}

-- Static methods

-- Return the string data type for this database adapter with a given size
{{ api.Column.string_type(255) }}

-- Return the numeric data type for this database adapter with a given precision and scale
{{ api.Column.numeric_type('numeric', 12, 4) }}

BigQuery columns​

The Column type is overridden as a BigQueryColumn in BigQuery dbt projects. This object works the same as the Column type described above, with the exception of extra properties and methods:

Properties​

  • fields: Returns the list of subfields contained within a field (if the column is a STRUCT)
  • mode: Returns the "mode" of the column, eg. REPEATED

Instance methods​

flatten(): Return a flattened list of BigQueryColumns in which subfields are expanded into their own columns. For example, this nested field:

[{"hits": {"pageviews": 1, "bounces": 0}}]

will be expanded to:

[{"hits.pageviews": 1, "hits.bounces": 0}]

Result objects​

The execution of a resource in dbt generates a Result object. This object contains information about the executed node, timing, status, and metadata returned by the adapter. At the end of an invocation, dbt records these objects in run_results.json.

  • node: Full object representation of the dbt resource (model, seed, snapshot, test) executed, including its unique_id
  • status: dbt's interpretation of runtime success, failure, or error
  • thread_id: Which thread executed this node? E.g. Thread-1
  • execution_time: Total time spent executing this node, measured in seconds.
  • timing: Array that breaks down execution time into steps (often compile + execute)
  • message: How dbt will report this result on the CLI, based on information returned from the database
  • adapter_response: Dictionary of metadata returned from the database, which varies by adapter. For example, success code, number of rows_affected, total bytes_processed, and so on. Not applicable for tests.
    • rows_affected returns the number of rows modified by the last statement executed. In cases where the query's row count can't be determined or isn't applicable (such as when creating a view), a standard value of -1 is returned for rowcount.
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