nushell/crates/nu-command/src/database/commands/limit.rs

use super::super::SQLiteDatabase;
use crate::database::values::dsl::ExprDb;
use nu_engine::CallExt;
use nu_protocol::{
    ast::Call,
    engine::{Command, EngineState, Stack},
    Category, Example, IntoPipelineData, PipelineData, ShellError, Signature, Span, SyntaxShape,
    Type, Value,
};
use sqlparser::ast::Statement;

#[derive(Clone)]
pub struct LimitDb;

impl Command for LimitDb {
    fn name(&self) -> &str {
        "limit"
    }

    fn usage(&self) -> &str {
        "Limit result from query"
    }

    fn signature(&self) -> Signature {
        Signature::build(self.name())
            .required(
                "limit",
                SyntaxShape::Int,
                "Number of rows to extract for query",
            )
            .input_type(Type::Custom("database".into()))
            .output_type(Type::Custom("database".into()))
            .category(Category::Custom("database".into()))
    }

    fn search_terms(&self) -> Vec<&str> {
        vec!["database", "head", "tail"]
    }

    fn examples(&self) -> Vec<Example> {
        vec![Example {
            description: "Limits selection from table",
            example: r#"open db.sqlite
    | from table table_a
    | select a
    | limit 10
    | describe"#,
            result: Some(Value::Record {
                cols: vec!["connection".into(), "query".into()],
                vals: vec![
                    Value::String {
                        val: "db.sqlite".into(),
                        span: Span::test_data(),
                    },
                    Value::String {
                        val: "SELECT a FROM table_a LIMIT 10".into(),
                        span: Span::test_data(),
                    },
                ],
                span: Span::test_data(),
            }),
        }]
    }

    fn run(
        &self,
        engine_state: &EngineState,
        stack: &mut Stack,
        call: &Call,
        input: PipelineData,
    ) -> Result<PipelineData, ShellError> {
        let limit: Value = call.req(engine_state, stack, 0)?;
        let expr = ExprDb::try_from_value(&limit)?.into_native();

        let mut db = SQLiteDatabase::try_from_pipeline(input, call.head)?;
        match db.statement {
            Some(ref mut statement) => match statement {
                Statement::Query(query) => query.as_mut().limit = Some(expr),
                s => {
                    return Err(ShellError::GenericError(
                        "Connection doesnt define a statement".into(),
                        format!("Expected a connection with query. Got {}", s),
                        Some(call.head),
                        None,
                        Vec::new(),
                    ))
                }
            },
            None => {
                return Err(ShellError::GenericError(
                    "Connection without query".into(),
                    "The connection needs a query defined".into(),
                    Some(call.head),
                    None,
                    Vec::new(),
                ))
            }
        };

        Ok(db.into_value(call.head).into_pipeline_data())
    }
}

#[cfg(test)]
mod test {
    use super::super::super::expressions::{FieldExpr, OrExpr};
    use super::super::{FromDb, ProjectionDb, WhereDb};
    use super::*;
    use crate::database::test_database::test_database;

    #[test]
    fn test_examples() {
        test_database(vec![
            Box::new(LimitDb {}),
            Box::new(ProjectionDb {}),
            Box::new(FromDb {}),
            Box::new(WhereDb {}),
            Box::new(FieldExpr {}),
            Box::new(OrExpr {}),
        ])
    }
}