rusqlite/column.rs
1use std::str;
2
3use crate::{Error, Result, Statement};
4
5/// Information about a column of a SQLite query.
6#[derive(Debug)]
7pub struct Column<'stmt> {
8 name: &'stmt str,
9 decl_type: Option<&'stmt str>,
10}
11
12impl Column<'_> {
13 /// Returns the name of the column.
14 #[inline]
15 #[must_use]
16 pub fn name(&self) -> &str {
17 self.name
18 }
19
20 /// Returns the type of the column (`None` for expression).
21 #[inline]
22 #[must_use]
23 pub fn decl_type(&self) -> Option<&str> {
24 self.decl_type
25 }
26}
27
28impl Statement<'_> {
29 /// Get all the column names in the result set of the prepared statement.
30 ///
31 /// If associated DB schema can be altered concurrently, you should make
32 /// sure that current statement has already been stepped once before
33 /// calling this method.
34 pub fn column_names(&self) -> Vec<&str> {
35 let n = self.column_count();
36 let mut cols = Vec::with_capacity(n as usize);
37 for i in 0..n {
38 let s = self.column_name_unwrap(i);
39 cols.push(s);
40 }
41 cols
42 }
43
44 /// Return the number of columns in the result set returned by the prepared
45 /// statement.
46 ///
47 /// If associated DB schema can be altered concurrently, you should make
48 /// sure that current statement has already been stepped once before
49 /// calling this method.
50 #[inline]
51 pub fn column_count(&self) -> usize {
52 self.stmt.column_count()
53 }
54
55 /// Check that column name reference lifetime is limited:
56 /// https://www.sqlite.org/c3ref/column_name.html
57 /// > The returned string pointer is valid...
58 ///
59 /// `column_name` reference can become invalid if `stmt` is reprepared
60 /// (because of schema change) when `query_row` is called. So we assert
61 /// that a compilation error happens if this reference is kept alive:
62 /// ```compile_fail
63 /// use rusqlite::{Connection, Result};
64 /// fn main() -> Result<()> {
65 /// let db = Connection::open_in_memory()?;
66 /// let mut stmt = db.prepare("SELECT 1 as x")?;
67 /// let column_name = stmt.column_name(0)?;
68 /// let x = stmt.query_row([], |r| r.get::<_, i64>(0))?; // E0502
69 /// assert_eq!(1, x);
70 /// assert_eq!("x", column_name);
71 /// Ok(())
72 /// }
73 /// ```
74 #[inline]
75 pub(super) fn column_name_unwrap(&self, col: usize) -> &str {
76 // Just panic if the bounds are wrong for now, we never call this
77 // without checking first.
78 self.column_name(col).expect("Column out of bounds")
79 }
80
81 /// Returns the name assigned to a particular column in the result set
82 /// returned by the prepared statement.
83 ///
84 /// If associated DB schema can be altered concurrently, you should make
85 /// sure that current statement has already been stepped once before
86 /// calling this method.
87 ///
88 /// ## Failure
89 ///
90 /// Returns an `Error::InvalidColumnIndex` if `idx` is outside the valid
91 /// column range for this row.
92 ///
93 /// Panics when column name is not valid UTF-8.
94 #[inline]
95 pub fn column_name(&self, col: usize) -> Result<&str> {
96 self.stmt
97 .column_name(col)
98 .ok_or(Error::InvalidColumnIndex(col))
99 .map(|slice| {
100 str::from_utf8(slice.to_bytes()).expect("Invalid UTF-8 sequence in column name")
101 })
102 }
103
104 /// Returns the column index in the result set for a given column name.
105 ///
106 /// If there is no AS clause then the name of the column is unspecified and
107 /// may change from one release of SQLite to the next.
108 ///
109 /// If associated DB schema can be altered concurrently, you should make
110 /// sure that current statement has already been stepped once before
111 /// calling this method.
112 ///
113 /// # Failure
114 ///
115 /// Will return an `Error::InvalidColumnName` when there is no column with
116 /// the specified `name`.
117 #[inline]
118 pub fn column_index(&self, name: &str) -> Result<usize> {
119 let bytes = name.as_bytes();
120 let n = self.column_count();
121 for i in 0..n {
122 // Note: `column_name` is only fallible if `i` is out of bounds,
123 // which we've already checked.
124 if bytes.eq_ignore_ascii_case(self.stmt.column_name(i).unwrap().to_bytes()) {
125 return Ok(i);
126 }
127 }
128 Err(Error::InvalidColumnName(String::from(name)))
129 }
130
131 /// Returns a slice describing the columns of the result of the query.
132 ///
133 /// If associated DB schema can be altered concurrently, you should make
134 /// sure that current statement has already been stepped once before
135 /// calling this method.
136 #[cfg(feature = "column_decltype")]
137 #[cfg_attr(docsrs, doc(cfg(feature = "column_decltype")))]
138 pub fn columns(&self) -> Vec<Column> {
139 let n = self.column_count();
140 let mut cols = Vec::with_capacity(n as usize);
141 for i in 0..n {
142 let name = self.column_name_unwrap(i);
143 let slice = self.stmt.column_decltype(i);
144 let decl_type = slice.map(|s| {
145 str::from_utf8(s.to_bytes()).expect("Invalid UTF-8 sequence in column declaration")
146 });
147 cols.push(Column { name, decl_type });
148 }
149 cols
150 }
151}
152
153#[cfg(test)]
154mod test {
155 use crate::{Connection, Result};
156
157 #[test]
158 #[cfg(feature = "column_decltype")]
159 fn test_columns() -> Result<()> {
160 use super::Column;
161
162 let db = Connection::open_in_memory()?;
163 let query = db.prepare("SELECT * FROM sqlite_master")?;
164 let columns = query.columns();
165 let column_names: Vec<&str> = columns.iter().map(Column::name).collect();
166 assert_eq!(
167 column_names.as_slice(),
168 &["type", "name", "tbl_name", "rootpage", "sql"]
169 );
170 let column_types: Vec<Option<String>> = columns
171 .iter()
172 .map(|col| col.decl_type().map(str::to_lowercase))
173 .collect();
174 assert_eq!(
175 &column_types[..3],
176 &[
177 Some("text".to_owned()),
178 Some("text".to_owned()),
179 Some("text".to_owned()),
180 ]
181 );
182 Ok(())
183 }
184
185 #[test]
186 fn test_column_name_in_error() -> Result<()> {
187 use crate::{types::Type, Error};
188 let db = Connection::open_in_memory()?;
189 db.execute_batch(
190 "BEGIN;
191 CREATE TABLE foo(x INTEGER, y TEXT);
192 INSERT INTO foo VALUES(4, NULL);
193 END;",
194 )?;
195 let mut stmt = db.prepare("SELECT x as renamed, y FROM foo")?;
196 let mut rows = stmt.query([])?;
197 let row = rows.next()?.unwrap();
198 match row.get::<_, String>(0).unwrap_err() {
199 Error::InvalidColumnType(idx, name, ty) => {
200 assert_eq!(idx, 0);
201 assert_eq!(name, "renamed");
202 assert_eq!(ty, Type::Integer);
203 }
204 e => {
205 panic!("Unexpected error type: {:?}", e);
206 }
207 }
208 match row.get::<_, String>("y").unwrap_err() {
209 Error::InvalidColumnType(idx, name, ty) => {
210 assert_eq!(idx, 1);
211 assert_eq!(name, "y");
212 assert_eq!(ty, Type::Null);
213 }
214 e => {
215 panic!("Unexpected error type: {:?}", e);
216 }
217 }
218 Ok(())
219 }
220
221 /// `column_name` reference should stay valid until `stmt` is reprepared (or
222 /// reset) even if DB schema is altered (SQLite documentation is
223 /// ambiguous here because it says reference "is valid until (...) the next
224 /// call to sqlite3_column_name() or sqlite3_column_name16() on the same
225 /// column.". We assume that reference is valid if only
226 /// `sqlite3_column_name()` is used):
227 #[test]
228 #[cfg(feature = "modern_sqlite")]
229 fn test_column_name_reference() -> Result<()> {
230 let db = Connection::open_in_memory()?;
231 db.execute_batch("CREATE TABLE y (x);")?;
232 let stmt = db.prepare("SELECT x FROM y;")?;
233 let column_name = stmt.column_name(0)?;
234 assert_eq!("x", column_name);
235 db.execute_batch("ALTER TABLE y RENAME COLUMN x TO z;")?;
236 // column name is not refreshed until statement is re-prepared
237 let same_column_name = stmt.column_name(0)?;
238 assert_eq!(same_column_name, column_name);
239 Ok(())
240 }
241}