|
| 1 | +# Linter guide |
| 2 | + |
| 3 | +Linting is a powerful tool for improving code quality and consistency. It enables you to automatically validate model definition, ensuring they adhere to your team's best practices. |
| 4 | + |
| 5 | +When a SQLMesh command is executed and the project is loaded, each model's code is checked for compliance with a set of rules you choose. |
| 6 | + |
| 7 | +SQLMesh provides built-in rules, and you can define custom rules. This improves code quality and helps detect issues early in the development cycle when they are simpler to debug. |
| 8 | + |
| 9 | +## Rules |
| 10 | + |
| 11 | +Each linting rule is responsible for identifying a pattern in a model's code. |
| 12 | + |
| 13 | +Some rules validate that a pattern is *not* present, such as not allowing `SELECT *` in a model's outermost query. Other rules validate that a pattern *is* present, like ensuring that every model's `owner` field is specified. We refer to both of these below as "validating a pattern". |
| 14 | + |
| 15 | +Rules are defined in Python. Each rule is an individual Python class that inherits from SQLMesh's `Rule` base class and defines the logic for validating a pattern. |
| 16 | + |
| 17 | +We display a portion of the `Rule` base class's code below ([full source code](https://github.com/TobikoData/sqlmesh/blob/main/sqlmesh/core/linter/rule.py)). Its methods and properties illustrate the most important components of the subclassed rules you define. |
| 18 | + |
| 19 | +Each rule class you create has four vital components: |
| 20 | + |
| 21 | +1. Name: the class's name is used as the rule's name. |
| 22 | +2. Description: the class should define a docstring that provides a short explanation of the rule's purpose. |
| 23 | +3. Pattern validation logic: the class should define a `check_model()` method containing the core logic that validates the rule's pattern. The method can access any `Model` attribute. |
| 24 | +4. Rule violation logic: if a rule's pattern is not validated, the rule is "violated" and the class should return a `RuleViolation` object. The `RuleViolation` object should include the contextual information a user needs to understand and fix the problem. |
| 25 | + |
| 26 | +``` python linenums="1" |
| 27 | +# Class name used as rule's name |
| 28 | +class Rule: |
| 29 | + # Docstring provides rule's description |
| 30 | + """The base class for a rule.""" |
| 31 | + |
| 32 | + # Pattern validation logic goes in `check_model()` method |
| 33 | + @abc.abstractmethod |
| 34 | + def check_model(self, model: Model) -> t.Optional[RuleViolation]: |
| 35 | + """The evaluation function that checks for a violation of this rule.""" |
| 36 | + |
| 37 | + # Rule violation object returned by `violation()` method |
| 38 | + def violation(self, violation_msg: t.Optional[str] = None) -> RuleViolation: |
| 39 | + """Return a RuleViolation instance if this rule is violated""" |
| 40 | + return RuleViolation(rule=self, violation_msg=violation_msg or self.summary) |
| 41 | +``` |
| 42 | + |
| 43 | +### Built-in rules |
| 44 | + |
| 45 | +SQLMesh includes a set of predefined rules that check for potential SQL errors or enforce code style. |
| 46 | + |
| 47 | +An example of the latter is the `NoSelectStar` rule, which prohibits a model from using `SELECT *` in its query's outer-most select statement. |
| 48 | + |
| 49 | +Here is code for the built-in `NoSelectStar` rule class, with the different components annotated: |
| 50 | + |
| 51 | +``` python linenums="1" |
| 52 | +# Rule's name is the class name `NoSelectStar` |
| 53 | +class NoSelectStar(Rule): |
| 54 | + # Docstring explaining rule |
| 55 | + """Query should not contain SELECT * on its outer most projections, even if it can be expanded.""" |
| 56 | + |
| 57 | + def check_model(self, model: Model) -> t.Optional[RuleViolation]: |
| 58 | + # If this model does not contain a SQL query, there is nothing to validate |
| 59 | + if not isinstance(model, SqlModel): |
| 60 | + return None |
| 61 | + |
| 62 | + # Use the query's `is_star` property to detect the `SELECT *` pattern. |
| 63 | + # If present, call the `violation()` method to return a `RuleViolation` object. |
| 64 | + return self.violation() if model.query.is_star else None |
| 65 | +``` |
| 66 | + |
| 67 | +Here are all of SQLMesh's built-in linting rules: |
| 68 | + |
| 69 | +| Name | Check type | Explanation | |
| 70 | +| -------------------------- | ----------- | ------------------------------------------------------------------------------------------------------------------------ | |
| 71 | +| ambiguousorinvalidcolumn | Correctness | SQLMesh found duplicate columns or was unable to determine whether a column is duplicated or not | |
| 72 | +| invalidselectstarexpansion | Correctness | The query's top-level selection may be `SELECT *`, but only if SQLMesh can expand the `SELECT *` into individual columns | |
| 73 | +| noselectstar | Stylistic | The query's top-level selection may not be `SELECT *`, even if SQLMesh can expand the `SELECT *` into individual columns | |
| 74 | + |
| 75 | + |
| 76 | +### User-defined rules |
| 77 | + |
| 78 | +You may define custom rules to implement your team's best practices. |
| 79 | + |
| 80 | +For instance, you could ensure all models have an `owner` by defining the following linting rule: |
| 81 | + |
| 82 | +``` python linenums="1" title="linter/user.py" |
| 83 | +import typing as t |
| 84 | + |
| 85 | +from sqlmesh.core.linter.rule import Rule, RuleViolation |
| 86 | +from sqlmesh.core.model import Model |
| 87 | + |
| 88 | +class NoMissingOwner(Rule): |
| 89 | + """Model owner should always be specified.""" |
| 90 | + |
| 91 | + def check_model(self, model: Model) -> t.Optional[RuleViolation]: |
| 92 | + # Rule violated if the model's owner field (`model.owner`) is not specified |
| 93 | + return self.violation() if not model.owner else None |
| 94 | + |
| 95 | +``` |
| 96 | + |
| 97 | +Place a rule's code in the project's `linter/` directory. SQLMesh will load all subclasses of `Rule` from that directory. |
| 98 | + |
| 99 | +If the rule is specified in the project's [configuration file](#applying-linting-rules), SQLMesh will run it when the project is loaded. All SQLMesh commands will load the project, except for `create_external_models`, `migrate`, `rollback`, `run`, `environments`, and `invalidate`. |
| 100 | + |
| 101 | +SQLMesh will error if a model violates the rule, informing you which model(s) violated the rule. In this example, `full_model.sql` violated the `NoMissingOwner` rule: |
| 102 | + |
| 103 | +``` bash |
| 104 | +$ sqlmesh plan |
| 105 | + |
| 106 | +Linter errors for .../models/full_model.sql: |
| 107 | + - nomissingowner: Model owner should always be specified. |
| 108 | + |
| 109 | +Error: Linter detected errors in the code. Please fix them before proceeding. |
| 110 | +``` |
| 111 | + |
| 112 | +## Applying linting rules |
| 113 | + |
| 114 | +Specify which linting rules a project should apply in the project's [configuration file](../guides/configuration.md). |
| 115 | + |
| 116 | +Rules are specified as lists of rule names under the `linter` key. Globally enable or disable linting with the `enabled` key, which is `false` by default. |
| 117 | + |
| 118 | +NOTE: you **must** set the `enabled` key to `true` key to apply the project's linting rules. |
| 119 | + |
| 120 | +### Specific linting rules |
| 121 | + |
| 122 | +This example specifies that the `"ambiguousorinvalidcolumn"` and `"invalidselectstarexpansion"` linting rules should be enforced: |
| 123 | + |
| 124 | +=== "YAML" |
| 125 | + |
| 126 | + ```yaml linenums="1" |
| 127 | + linter: |
| 128 | + enabled: true |
| 129 | + rules: ["ambiguousorinvalidcolumn", "invalidselectstarexpansion"] |
| 130 | + ``` |
| 131 | + |
| 132 | +=== "Python" |
| 133 | + |
| 134 | + ```python linenums="1" |
| 135 | + from sqlmesh.core.config import Config, LinterConfig |
| 136 | + |
| 137 | + config = Config( |
| 138 | + linter=LinterConfig( |
| 139 | + enabled=True, |
| 140 | + rules=["ambiguousorinvalidcolumn", "invalidselectstarexpansion"] |
| 141 | + ) |
| 142 | + ) |
| 143 | + ``` |
| 144 | + |
| 145 | +### All linting rules |
| 146 | + |
| 147 | +Apply every built-in and user-defined rule by specifying `"ALL"` instead of a list of rules: |
| 148 | + |
| 149 | +=== "YAML" |
| 150 | + |
| 151 | + ```yaml linenums="1" |
| 152 | + linter: |
| 153 | + enabled: True |
| 154 | + rules: "ALL" |
| 155 | + ``` |
| 156 | + |
| 157 | +=== "Python" |
| 158 | + |
| 159 | + ```python linenums="1" |
| 160 | + from sqlmesh.core.config import Config, LinterConfig |
| 161 | + |
| 162 | + config = Config( |
| 163 | + linter=LinterConfig( |
| 164 | + enabled=True, |
| 165 | + rules="all", |
| 166 | + ) |
| 167 | + ) |
| 168 | + ``` |
| 169 | + |
| 170 | +If you want to apply all rules except for a few, you can specify `"ALL"` and list the rules to ignore in the `ignored_rules` key: |
| 171 | + |
| 172 | +=== "YAML" |
| 173 | + |
| 174 | + ```yaml linenums="1" |
| 175 | + linter: |
| 176 | + enabled: True |
| 177 | + rules: "ALL" # apply all built-in and user-defined rules and error if violated |
| 178 | + ignored_rules: ["noselectstar"] # but don't run the `noselectstar` rule |
| 179 | + ``` |
| 180 | + |
| 181 | +=== "Python" |
| 182 | + |
| 183 | + ```python linenums="1" |
| 184 | + from sqlmesh.core.config import Config, LinterConfig |
| 185 | + |
| 186 | + config = Config( |
| 187 | + linter=LinterConfig( |
| 188 | + enabled=True, |
| 189 | + # apply all built-in and user-defined linting rules and error if violated |
| 190 | + rules="all", |
| 191 | + # but don't run the `noselectstar` rule |
| 192 | + ignored_rules=["noselectstar"] |
| 193 | + ) |
| 194 | + ) |
| 195 | + ``` |
| 196 | + |
| 197 | +### Exclude a model from linting |
| 198 | + |
| 199 | +You can specify that a specific *model* ignore a linting rule by specifying `ignored_rules` in its `MODEL` block. |
| 200 | + |
| 201 | +This example specifies that the model `docs_example.full_model` should not run the `invalidselectstarexpansion` rule: |
| 202 | + |
| 203 | +```sql linenums="1" |
| 204 | +MODEL( |
| 205 | + name docs_example.full_model, |
| 206 | + ignored_rules: ["invalidselectstarexpansion"] # or "ALL" to turn off linting completely |
| 207 | +); |
| 208 | +``` |
| 209 | + |
| 210 | +### Rule violation behavior |
| 211 | + |
| 212 | +Linting rule violations raise an error by default, preventing the project from running until the violation is addressed. |
| 213 | + |
| 214 | +You may specify that a rule's violation should not error and only log a warning by specifying it in the `warning_rules` key instead of the `rules` key. |
| 215 | + |
| 216 | +=== "YAML" |
| 217 | + |
| 218 | + ```yaml linenums="1" |
| 219 | + linter: |
| 220 | + enabled: True |
| 221 | + # error if `ambiguousorinvalidcolumn` rule violated |
| 222 | + rules: ["ambiguousorinvalidcolumn"] |
| 223 | + # but only warn if "invalidselectstarexpansion" is violated |
| 224 | + warning_rules: ["invalidselectstarexpansion"] |
| 225 | + ``` |
| 226 | + |
| 227 | +=== "Python" |
| 228 | + |
| 229 | + ```python linenums="1" |
| 230 | + from sqlmesh.core.config import Config, LinterConfig |
| 231 | + |
| 232 | + config = Config( |
| 233 | + linter=LinterConfig( |
| 234 | + enabled=True, |
| 235 | + # error if `ambiguousorinvalidcolumn` rule violated |
| 236 | + rules=["ambiguousorinvalidcolumn"], |
| 237 | + # but only warn if "invalidselectstarexpansion" is violated |
| 238 | + warning_rules=["invalidselectstarexpansion"], |
| 239 | + ) |
| 240 | + ) |
| 241 | + ``` |
| 242 | + |
| 243 | +SQLMesh will raise an error if the same rule is included in more than one of the `rules`, `warning_rules`, and `ignored_rules` keys since they should be mutually exclusive. |
0 commit comments