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SQLTraverse is AST (abstract syntax tree) walker. This allows you to move through the AST generated by the Codeschool sqlite-parser in a structured manner. If you've ever used Estraverse before it works in the exact same way (in fact we use Estraverse under the hood).
The following code will do a simple walk of the AST passed to it. We can take actions either when we enter the node or when we leave the node.
sqltraverse.traverse(ast, {
enter: function (node, parent) {
if (node.type == 'statement' || node.type == 'assignment')
return sqltraverse.VisitorOption.Skip;
},
leave: function (node, parent) {
if (node.type == 'literal')
console.log(node.value);
}
});We can use this.skip, this.remove and this.break functions instead of using Skip, Remove and Break.
sqltraverse.traverse(ast, {
enter: function (node) {
this.break();
}
});And sqltraverse provides sqltraverse.replace function. When returning node from enter/leave, current node is replaced with it.
result = sqltraverse.replace(tree, {
enter: function (node) {
// Replace it with replaced.
if (node.type === 'literal')
return replaced;
}
});By passing visitor.keys mapping, we can extend sqltraverse traversing functionality.
// This tree contains a user-defined `TestExpression` node.
var tree = {
type: 'TestExpression',
// This 'argument' is the property containing the other **node**.
argument: {
type: 'literal',
value: 20
},
// This 'extended' is the property not containing the other **node**.
extended: true
};
sqltraverse.traverse(tree, {
enter: function (node) { },
// Extending the existing traversing rules.
keys: {
// TargetNodeName: [ 'keys', 'containing', 'the', 'other', '**node**' ]
TestExpression: ['argument']
}
});By passing visitor.fallback option, we can control the behavior when encountering unknown nodes.
// This tree contains a user-defined `TestExpression` node.
var tree = {
type: 'TestExpression',
// This 'argument' is the property containing the other **node**.
argument: {
type: 'literal',
value: 20
},
// This 'extended' is the property not containing the other **node**.
extended: true
};
sqltraverse.traverse(tree, {
enter: function (node) { },
// Iterating the child **nodes** of unknown nodes.
fallback: 'iteration'
});When visitor.fallback is a function, we can determine which keys to visit on each node.
// This tree contains a user-defined `TestExpression` node.
var tree = {
type: 'TestExpression',
// This 'argument' is the property containing the other **node**.
argument: {
type: 'literal',
value: 20
},
// This 'extended' is the property not containing the other **node**.
extended: true
};
sqltraverse.traverse(tree, {
enter: function (node) { },
// Skip the `argument` property of each node
fallback: function(node) {
return Object.keys(node).filter(function(key) {
return key !== 'argument';
});
}
});
Copyright (c) 2016
- Tests, tests and more tests.
- Documentation currently under construction (The examples need to be worked through for SQL instead of JavaScript).
- AST is currently in a state of flux for some node types. We also probably need a builder for these nodes (another project).
- You need to pass in
ast.statementand not just the rawastgiven back from the parser. (This is an issue with the base node not having a type.)
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