From 621555af37594a213d91ea113d5fc7739af84d40 Mon Sep 17 00:00:00 2001 From: Daniel Baumann Date: Wed, 4 Jan 2023 08:24:05 +0100 Subject: Adding upstream version 10.4.2. Signed-off-by: Daniel Baumann --- pdoc/docs/expressions.md | 41 +++++++++++++++++++++++++++++++++++++++++ 1 file changed, 41 insertions(+) create mode 100644 pdoc/docs/expressions.md (limited to 'pdoc/docs/expressions.md') diff --git a/pdoc/docs/expressions.md b/pdoc/docs/expressions.md new file mode 100644 index 0000000..c82674b --- /dev/null +++ b/pdoc/docs/expressions.md @@ -0,0 +1,41 @@ +# Expressions + +Every AST node in SQLGlot is represented by a subclass of `Expression`. Each such expression encapsulates any necessary context, such as its child expressions, their names, or arg keys, and whether each child expression is optional or not. + +Furthermore, the following attributes are common across all expressions: + +#### key + +A unique key for each class in the `Expression` hierarchy. This is useful for hashing and representing expressions as strings. + +#### args + +A dictionary used for mapping child arg keys, to the corresponding expressions. A value in this mapping is usually either a single or a list of `Expression` instances, but SQLGlot doesn't impose any constraints on the actual type of the value. + +#### arg_types + +A dictionary used for mapping arg keys to booleans that determine whether the corresponding expressions are optional or not. Consider the following example: + +```python +class Limit(Expression): + arg_types = {"this": False, "expression": True} + +``` + +Here, `Limit` declares that it expects to have one optional and one required child expression, which can be referenced through `this` and `expression`, respectively. The arg keys are generally arbitrary, but there are helper methods for keys like `this`, `expression` and `expressions` that abstract away dictionary lookups and related checks. For this reason, these keys are common throughout SQLGlot's codebase. + +#### parent + +A reference to the parent expression (may be `None`). + +#### arg_key + +The arg key an expression is associated with, i.e. the name its parent expression uses to refer to it. + +#### comments + +A list of comments that are associated with a given expression. This is used in order to preserve comments when transpiling SQL code. + +#### type + +The data type of an expression, as inferred by SQLGlot's optimizer. -- cgit v1.2.3