Metadata contains definitions of tables and associated objects such as index, view, triggers, etc. Hence an object of MetaData class from SQLAlchemy Metadata is a collection of Table objects and their associated schema constructs. It holds a collection of Table objects as well as an optional binding to an Engine or Connection.
Full Answer
What is object metadata in SQLAlchemy?
Of course by typing type (metadata) I get exactly what type of object metadata is: sqlalchemy.sql.schema.MetaData. In SQLAlchemy documentation it is written MetaData is a container object that keeps together many different features of a database (or multiple databases) being described.
What is a database table in SQLAlchemy?
So database tables in SQLAlchemy belong (are linked to) a metadata object. The table adds itself to the metadata; there is a tables property on the metadata object that acts a lot like a list:
What are the object of database metadata in Python?
The most fundamental objects of Database MetaData are MetaData, Table, and Column. The queries in a relational database are usually created on a Table of a database. These tables are represented as Table objects in Python SQLAlchemy named as Table.
Is metadata a function or something else?
Is MetaData () a function or something else? According to SQLAlchemy documentation MetaData is: a container object that keeps together many different features of a database (or multiple databases) being described. But if it is an object so then how can it be run as something similar to a function: Metadata ()?
What Does metadata do in SQLAlchemy?
Metadata contains definitions of tables and associated objects such as index, view, triggers, etc. Hence an object of MetaData class from SQLAlchemy Metadata is a collection of Table objects and their associated schema constructs.
What is metadata in database?
A meta data is the data about the data. It is the self-describing nature of databases. It holds the information about each data element in the database. Such as names, types, range of values, access authorization, indicate which application program uses the data.
What is ORM metadata?
The ORM uses the metadata to generate the code used to access the tables. For example, if it's a date column then it generates the code to deal with that column as a date. It will read foreign keys and primary keys to build relationships in the code as well as for generating the proper SQL syntax.
What does base metadata Create_all do?
create_all() creates foreign key constraints between tables usually inline with the table definition itself, and for this reason it also generates the tables in order of their dependency.
What is metadata with example?
Metadata makes finding and working with data easier – allowing the user to sort or locate specific documents. Some examples of basic metadata are author, date created, date modified, and file size. Metadata is also used for unstructured data such as images, video, web pages, spreadsheets, etc.
What is metadata and its uses?
Metadata represents data about data. Metadata enriches the data with information that makes it easier to find, use and manage. For instance, HTML tags define layout for human readers. Semantic metadata helps computers to interpret data by adding references to concepts in a knowledge graph.
What is base in sqlalchemy?
A base class stores a catlog of classes and mapped tables in the Declarative system. This is called as the declarative base class. There will be usually just one instance of this base in a commonly imported module. The declarative_base() function is used to create base class. This function is defined in sqlalchemy.
What is ORM and why it is used?
What is an ORM? An object-relational mapper provides an object-oriented layer between relational databases and object-oriented programming languages without having to write SQL queries. It standardizes interfaces reducing boilerplate and speeding development time.
Is ORM better than SQL?
ORM and SQL are two tools available that web developers can use in database management. When comparing them, SQL has a higher hands-on management than ORM. Because ORM has a higher level of abstraction and more complexity than SQL, less hands-on management is required; this makes data management more efficient.
What is metadata in SQL?
Metadata in simple words describe as data about data. Usually, the metadata returns the information about the database, db objects, db files, etc., in the SQL server.
What is reflection in SQLAlchemy?
A Table object can be instructed to load information about itself from the corresponding database schema object already existing within the database. This process is called reflection.
How do I get column names in SQLAlchemy?
To access the column names we can use the method keys() on the result. It returns a list of column names. Since, we queried only three columns, we can view the same columns on the output as well.
Describing Databases with MetaData: SQLAlchemy Core
The queries in a relational database are usually created on a Table of a database. These tables are represented as Table objects in Python SQLAlchemy named as Table. The MetaData is an object which consists of Table objects keyed to their string names. The syntax of creating a MetaData object is as below:
Accessing Tables and Columns
The columns of a Table are usually stored in an associative array i.e., Table.c, and can be accessed using “c” as shown in the following examples.
Accessing tables and keys using MetaData object
The metadata object can be used to access all the tables stored in the metadata object as shown in the below examples:
Declaring Constraints
As you can see we have declared the first Column as a primary key in the student_table. Running the following command will show the details of the primary key constraint.
Creating and Dropping Tables
So far we have created two Tables with a set of Columns and constraints. The next thing is we have to emit DDL to the SQLite database (in this case) so that we can query with the tables. This can be done as shown below:
Describing Databases with MetaData: SQLAlchemy ORM
We will learn how to create the same tables as we have created using Core with ORM. The ORM consists of mapped classes. The mapped classes are declared in the same manner as any Python class is created and we link the attributes of the mapped classes to the Columns of the Table.
