Merge pull request #196 from jgallagher/gwenn-invalid-column-type

Better error reporting on invalid column type.

Changelog.md

@@ -9,6 +9,9 @@
   and `query_row_named` now expects a `&Row` instead of a `Row`. The vast majority of calls
   to these functions will probably not need to change; see
   https://github.com/jgallagher/rusqlite/pull/184.
+* BREAKING CHANGE: A few cases of the `Error` enum have sprouted additional information
+  (e.g., `FromSqlConversionFailure` now also includes the column index and the type returned
+  by SQLite).
 * Added `#[deprecated(since = "...", note = "...")]` flags (new in Rust 1.9 for libraries) to
   all deprecated APIs.
 * Added `query_row` convenience function to `Statement`.

src/error.rs

@@ -4,6 +4,7 @@ use std::path::PathBuf;
 use std::str;
 use libc::c_int;
 use {ffi, errmsg_to_string};
+use types::Type;
 
 /// Old name for `Error`. `SqliteError` is deprecated.
 #[deprecated(since = "0.6.0", note = "Use Error instead")]
@@ -19,8 +20,9 @@ pub enum Error {
     /// allow single-threaded use only.
     SqliteSingleThreadedMode,
 
-    /// An error case available for implementors of the `FromSql` trait.
+    /// Error when the value of a particular column is requested, but it cannot be converted to
-    FromSqlConversionFailure(Box<error::Error + Send + Sync>),
+    /// the requested Rust type.
+    FromSqlConversionFailure(usize, Type, Box<error::Error + Send + Sync>),
 
     /// Error converting a string to UTF-8.
     Utf8Error(str::Utf8Error),
@@ -51,7 +53,7 @@ pub enum Error {
 
     /// Error when the value of a particular column is requested, but the type of the result in
     /// that column cannot be converted to the requested Rust type.
-    InvalidColumnType,
+    InvalidColumnType(c_int, Type),
 
     /// Error when a query that was expected to insert one row did not insert any or insert many.
     StatementChangedRows(c_int),
@@ -59,7 +61,7 @@ pub enum Error {
     /// Error returned by `functions::Context::get` when the function argument cannot be converted
     /// to the requested type.
     #[cfg(feature = "functions")]
-    InvalidFunctionParameterType,
+    InvalidFunctionParameterType(usize, Type),
 
     /// An error case available for implementors of custom user functions (e.g.,
     /// `create_scalar_function`).
@@ -89,7 +91,13 @@ impl fmt::Display for Error {
                 write!(f,
                        "SQLite was compiled or configured for single-threaded use only")
             }
-            Error::FromSqlConversionFailure(ref err) => err.fmt(f),
+            Error::FromSqlConversionFailure(i, ref t, ref err) => {
+                write!(f,
+                       "Conversion error from type {} at index: {}, {}",
+                       t,
+                       i,
+                       err)
+            }
             Error::Utf8Error(ref err) => err.fmt(f),
             Error::NulError(ref err) => err.fmt(f),
             Error::InvalidParameterName(ref name) => write!(f, "Invalid parameter name: {}", name),
@@ -100,11 +108,15 @@ impl fmt::Display for Error {
             Error::QueryReturnedNoRows => write!(f, "Query returned no rows"),
             Error::InvalidColumnIndex(i) => write!(f, "Invalid column index: {}", i),
             Error::InvalidColumnName(ref name) => write!(f, "Invalid column name: {}", name),
-            Error::InvalidColumnType => write!(f, "Invalid column type"),
+            Error::InvalidColumnType(i, ref t) => {
+                write!(f, "Invalid column type {} at index: {}", t, i)
+            }
             Error::StatementChangedRows(i) => write!(f, "Query changed {} rows", i),
 
             #[cfg(feature = "functions")]
-            Error::InvalidFunctionParameterType => write!(f, "Invalid function parameter type"),
+            Error::InvalidFunctionParameterType(i, ref t) => {
+                write!(f, "Invalid function parameter type {} at index {}", t, i)
+            }
             #[cfg(feature = "functions")]
             Error::UserFunctionError(ref err) => err.fmt(f),
         }
@@ -119,7 +131,7 @@ impl error::Error for Error {
             Error::SqliteSingleThreadedMode => {
                 "SQLite was compiled or configured for single-threaded use only"
             }
-            Error::FromSqlConversionFailure(ref err) => err.description(),
+            Error::FromSqlConversionFailure(_, _, ref err) => err.description(),
             Error::Utf8Error(ref err) => err.description(),
             Error::InvalidParameterName(_) => "invalid parameter name",
             Error::NulError(ref err) => err.description(),
@@ -130,11 +142,11 @@ impl error::Error for Error {
             Error::QueryReturnedNoRows => "query returned no rows",
             Error::InvalidColumnIndex(_) => "invalid column index",
             Error::InvalidColumnName(_) => "invalid column name",
-            Error::InvalidColumnType => "invalid column type",
+            Error::InvalidColumnType(_, _) => "invalid column type",
             Error::StatementChangedRows(_) => "query inserted zero or more than one row",
 
             #[cfg(feature = "functions")]
-            Error::InvalidFunctionParameterType => "invalid function parameter type",
+            Error::InvalidFunctionParameterType(_, _) => "invalid function parameter type",
             #[cfg(feature = "functions")]
             Error::UserFunctionError(ref err) => err.description(),
         }
@@ -144,7 +156,7 @@ impl error::Error for Error {
     fn cause(&self) -> Option<&error::Error> {
         match *self {
             Error::SqliteFailure(ref err, _) => Some(err),
-            Error::FromSqlConversionFailure(ref err) => Some(&**err),
+            Error::FromSqlConversionFailure(_, _, ref err) => Some(&**err),
             Error::Utf8Error(ref err) => Some(err),
             Error::NulError(ref err) => Some(err),
 
@@ -154,12 +166,12 @@ impl error::Error for Error {
             Error::QueryReturnedNoRows |
             Error::InvalidColumnIndex(_) |
             Error::InvalidColumnName(_) |
-            Error::InvalidColumnType |
+            Error::InvalidColumnType(_, _) |
             Error::InvalidPath(_) |
             Error::StatementChangedRows(_) => None,
 
             #[cfg(feature = "functions")]
-            Error::InvalidFunctionParameterType => None,
+            Error::InvalidFunctionParameterType(_, _) => None,
 
             #[cfg(feature = "functions")]
             Error::UserFunctionError(ref err) => Some(&**err),

src/functions.rs

@@ -60,7 +60,7 @@ use ffi;
 use ffi::sqlite3_context;
 use ffi::sqlite3_value;
 
-use types::{ToSql, ToSqlOutput, FromSql, ValueRef};
+use types::{ToSql, ToSqlOutput, FromSql, FromSqlError, ValueRef};
 
 use {Result, Error, Connection, str_to_cstring, InnerConnection};
 
@@ -195,8 +195,12 @@ impl<'a> Context<'a> {
         let arg = self.args[idx];
         let value = unsafe { ValueRef::from_value(arg) };
         FromSql::column_result(value).map_err(|err| match err {
-            Error::InvalidColumnType => Error::InvalidFunctionParameterType,
+            FromSqlError::InvalidType => {
-            _ => err,
+                Error::InvalidFunctionParameterType(idx, value.data_type())
+            }
+            FromSqlError::Other(err) => {
+                Error::FromSqlConversionFailure(idx, value.data_type(), err)
+            }
         })
     }
 

src/lib.rs

@@ -73,7 +73,7 @@ use std::result;
 use std::str;
 use libc::{c_int, c_char, c_void};
 
-use types::{ToSql, ToSqlOutput, FromSql, ValueRef};
+use types::{ToSql, ToSqlOutput, FromSql, FromSqlError, ValueRef};
 use error::{error_from_sqlite_code, error_from_handle};
 use raw_statement::RawStatement;
 use cache::StatementCache;
@@ -1112,7 +1112,12 @@ impl<'a, 'stmt> Row<'a, 'stmt> {
     pub fn get_checked<I: RowIndex, T: FromSql>(&self, idx: I) -> Result<T> {
         let idx = try!(idx.idx(self.stmt));
         let value = unsafe { ValueRef::new(&self.stmt.stmt, idx) };
-        FromSql::column_result(value)
+        FromSql::column_result(value).map_err(|err| match err {
+            FromSqlError::InvalidType => Error::InvalidColumnType(idx, value.data_type()),
+            FromSqlError::Other(err) => {
+                Error::FromSqlConversionFailure(idx as usize, value.data_type(), err)
+            }
+        })
     }
 
     /// Return the number of columns in the current row.
@@ -1178,7 +1183,6 @@ impl<'a> ValueRef<'a> {
                     // The return value from sqlite3_column_blob() for a zero-length BLOB is a NULL pointer.
                     ValueRef::Blob(&[])
                 }
-
             }
             _ => unreachable!("sqlite3_column_type returned invalid value"),
         }
@@ -1540,7 +1544,7 @@ mod test {
                 .collect();
 
             match bad_type.unwrap_err() {
-                Error::InvalidColumnType => (),
+                Error::InvalidColumnType(_, _) => (),
                 err => panic!("Unexpected error {}", err),
             }
 
@@ -1600,7 +1604,7 @@ mod test {
                 .collect();
 
             match bad_type.unwrap_err() {
-                CustomError::Sqlite(Error::InvalidColumnType) => (),
+                CustomError::Sqlite(Error::InvalidColumnType(_, _)) => (),
                 err => panic!("Unexpected error {}", err),
             }
 
@@ -1662,7 +1666,7 @@ mod test {
             });
 
             match bad_type.unwrap_err() {
-                CustomError::Sqlite(Error::InvalidColumnType) => (),
+                CustomError::Sqlite(Error::InvalidColumnType(_, _)) => (),
                 err => panic!("Unexpected error {}", err),
             }
 

src/types/chrono.rs

@@ -5,8 +5,8 @@ use std::borrow::Cow;
 
 use self::chrono::{NaiveDate, NaiveTime, NaiveDateTime, DateTime, TimeZone, UTC, Local};
 
-use {Error, Result};
+use ::Result;
-use types::{FromSql, ToSql, ToSqlOutput, ValueRef};
+use types::{FromSql, FromSqlError, FromSqlResult, ToSql, ToSqlOutput, ValueRef};
 
 /// ISO 8601 calendar date without timezone => "YYYY-MM-DD"
 impl ToSql for NaiveDate {
@@ -18,10 +18,10 @@ impl ToSql for NaiveDate {
 
 /// "YYYY-MM-DD" => ISO 8601 calendar date without timezone.
 impl FromSql for NaiveDate {
-    fn column_result(value: ValueRef) -> Result<Self> {
+    fn column_result(value: ValueRef) -> FromSqlResult<Self> {
         value.as_str().and_then(|s| match NaiveDate::parse_from_str(s, "%Y-%m-%d") {
             Ok(dt) => Ok(dt),
-            Err(err) => Err(Error::FromSqlConversionFailure(Box::new(err))),
+            Err(err) => Err(FromSqlError::Other(Box::new(err))),
         })
     }
 }
@@ -36,7 +36,7 @@ impl ToSql for NaiveTime {
 
 /// "HH:MM"/"HH:MM:SS"/"HH:MM:SS.SSS" => ISO 8601 time without timezone.
 impl FromSql for NaiveTime {
-    fn column_result(value: ValueRef) -> Result<Self> {
+    fn column_result(value: ValueRef) -> FromSqlResult<Self> {
         value.as_str().and_then(|s| {
             let fmt = match s.len() {
                 5 => "%H:%M",
@@ -45,7 +45,7 @@ impl FromSql for NaiveTime {
             };
             match NaiveTime::parse_from_str(s, fmt) {
                 Ok(dt) => Ok(dt),
-                Err(err) => Err(Error::FromSqlConversionFailure(Box::new(err))),
+                Err(err) => Err(FromSqlError::Other(Box::new(err))),
             }
         })
     }
@@ -62,7 +62,7 @@ impl ToSql for NaiveDateTime {
 /// "YYYY-MM-DD HH:MM:SS"/"YYYY-MM-DD HH:MM:SS.SSS" => ISO 8601 combined date and time
 /// without timezone. ("YYYY-MM-DDTHH:MM:SS"/"YYYY-MM-DDTHH:MM:SS.SSS" also supported)
 impl FromSql for NaiveDateTime {
-    fn column_result(value: ValueRef) -> Result<Self> {
+    fn column_result(value: ValueRef) -> FromSqlResult<Self> {
         value.as_str().and_then(|s| {
             let fmt = if s.len() >= 11 && s.as_bytes()[10] == b'T' {
                 "%Y-%m-%dT%H:%M:%S%.f"
@@ -72,7 +72,7 @@ impl FromSql for NaiveDateTime {
 
             match NaiveDateTime::parse_from_str(s, fmt) {
                 Ok(dt) => Ok(dt),
-                Err(err) => Err(Error::FromSqlConversionFailure(Box::new(err))),
+                Err(err) => Err(FromSqlError::Other(Box::new(err))),
             }
         })
     }
@@ -87,7 +87,7 @@ impl<Tz: TimeZone> ToSql for DateTime<Tz> {
 
 /// RFC3339 ("YYYY-MM-DDTHH:MM:SS.SSS[+-]HH:MM") into DateTime<UTC>.
 impl FromSql for DateTime<UTC> {
-    fn column_result(value: ValueRef) -> Result<Self> {
+    fn column_result(value: ValueRef) -> FromSqlResult<Self> {
         {
             // Try to parse value as rfc3339 first.
             let s = try!(value.as_str());
@@ -117,7 +117,7 @@ impl FromSql for DateTime<UTC> {
 
 /// RFC3339 ("YYYY-MM-DDTHH:MM:SS.SSS[+-]HH:MM") into DateTime<Local>.
 impl FromSql for DateTime<Local> {
-    fn column_result(value: ValueRef) -> Result<Self> {
+    fn column_result(value: ValueRef) -> FromSqlResult<Self> {
         let utc_dt = try!(DateTime::<UTC>::column_result(value));
         Ok(utc_dt.with_timezone(&Local))
     }

src/types/from_sql.rs

@@ -1,36 +1,75 @@
 use super::{ValueRef, Value};
-use ::Result;
+use std::error::Error;
-use ::error::Error;
+use std::fmt;
+
+/// Enum listing possible errors from `FromSql` trait.
+#[derive(Debug)]
+pub enum FromSqlError {
+    /// Error when an SQLite value is requested, but the type of the result cannot be converted to the
+    /// requested Rust type.
+    InvalidType,
+    /// An error case available for implementors of the `FromSql` trait.
+    Other(Box<Error + Send + Sync>),
+}
+
+impl fmt::Display for FromSqlError {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        match *self {
+            FromSqlError::InvalidType => write!(f, "Invalid type"),
+            FromSqlError::Other(ref err) => err.fmt(f),
+        }
+    }
+}
+
+impl Error for FromSqlError {
+    fn description(&self) -> &str {
+        match *self {
+            FromSqlError::InvalidType => "invalid type",
+            FromSqlError::Other(ref err) => err.description(),
+        }
+    }
+
+    #[cfg_attr(feature="clippy", allow(match_same_arms))]
+    fn cause(&self) -> Option<&Error> {
+        match *self {
+            FromSqlError::InvalidType => None,
+            FromSqlError::Other(ref err) => err.cause(),
+        }
+    }
+}
+
+/// Result type for implementors of the `FromSql` trait.
+pub type FromSqlResult<T> = Result<T, FromSqlError>;
 
 /// A trait for types that can be created from a SQLite value.
 pub trait FromSql: Sized {
-    fn column_result(value: ValueRef) -> Result<Self>;
+    fn column_result(value: ValueRef) -> FromSqlResult<Self>;
 }
 
 impl FromSql for i32 {
-    fn column_result(value: ValueRef) -> Result<Self> {
+    fn column_result(value: ValueRef) -> FromSqlResult<Self> {
         i64::column_result(value).map(|i| i as i32)
     }
 }
 
 impl FromSql for i64 {
-    fn column_result(value: ValueRef) -> Result<Self> {
+    fn column_result(value: ValueRef) -> FromSqlResult<Self> {
         value.as_i64()
     }
 }
 
 impl FromSql for f64 {
-    fn column_result(value: ValueRef) -> Result<Self> {
+    fn column_result(value: ValueRef) -> FromSqlResult<Self> {
         match value {
             ValueRef::Integer(i) => Ok(i as f64),
             ValueRef::Real(f) => Ok(f),
-            _ => Err(Error::InvalidColumnType),
+            _ => Err(FromSqlError::InvalidType),
         }
     }
 }
 
 impl FromSql for bool {
-    fn column_result(value: ValueRef) -> Result<Self> {
+    fn column_result(value: ValueRef) -> FromSqlResult<Self> {
         i64::column_result(value).map(|i| match i {
             0 => false,
             _ => true,
@@ -39,19 +78,19 @@ impl FromSql for bool {
 }
 
 impl FromSql for String {
-    fn column_result(value: ValueRef) -> Result<Self> {
+    fn column_result(value: ValueRef) -> FromSqlResult<Self> {
         value.as_str().map(|s| s.to_string())
     }
 }
 
 impl FromSql for Vec<u8> {
-    fn column_result(value: ValueRef) -> Result<Self> {
+    fn column_result(value: ValueRef) -> FromSqlResult<Self> {
         value.as_blob().map(|b| b.to_vec())
     }
 }
 
 impl<T: FromSql> FromSql for Option<T> {
-    fn column_result(value: ValueRef) -> Result<Self> {
+    fn column_result(value: ValueRef) -> FromSqlResult<Self> {
         match value {
             ValueRef::Null => Ok(None),
             _ => FromSql::column_result(value).map(Some),
@@ -60,7 +99,7 @@ impl<T: FromSql> FromSql for Option<T> {
 }
 
 impl FromSql for Value {
-    fn column_result(value: ValueRef) -> Result<Self> {
+    fn column_result(value: ValueRef) -> FromSqlResult<Self> {
         Ok(value.into())
     }
 }

src/types/mod.rs

@@ -50,11 +50,13 @@
 //! `FromSql` for the cases where you want to know if a value was NULL (which gets translated to
 //! `None`).
 
-pub use self::from_sql::FromSql;
+pub use self::from_sql::{FromSql, FromSqlError, FromSqlResult};
 pub use self::to_sql::{ToSql, ToSqlOutput};
 pub use self::value::Value;
 pub use self::value_ref::ValueRef;
 
+use std::fmt;
+
 mod value;
 mod value_ref;
 mod from_sql;
@@ -84,6 +86,27 @@ mod serde_json;
 #[derive(Copy,Clone)]
 pub struct Null;
 
+#[derive(Clone,Debug,PartialEq)]
+pub enum Type {
+    Null,
+    Integer,
+    Real,
+    Text,
+    Blob,
+}
+
+impl fmt::Display for Type {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        match *self {
+            Type::Null => write!(f, "Null"),
+            Type::Integer => write!(f, "Integer"),
+            Type::Real => write!(f, "Real"),
+            Type::Text => write!(f, "Text"),
+            Type::Blob => write!(f, "Blob"),
+        }
+    }
+}
+
 #[cfg(test)]
 #[cfg_attr(feature="clippy", allow(similar_names))]
 mod test {
@@ -190,7 +213,7 @@ mod test {
     fn test_mismatched_types() {
         fn is_invalid_column_type(err: Error) -> bool {
             match err {
-                Error::InvalidColumnType => true,
+                Error::InvalidColumnType(_, _) => true,
                 _ => false,
             }
         }

src/types/serde_json.rs

@@ -3,8 +3,8 @@ extern crate serde_json;
 
 use self::serde_json::Value;
 
-use {Error, Result};
+use ::Result;
-use types::{FromSql, ToSql, ToSqlOutput, ValueRef};
+use types::{FromSql, FromSqlError, FromSqlResult, ToSql, ToSqlOutput, ValueRef};
 
 /// Serialize JSON `Value` to text.
 impl ToSql for Value {
@@ -15,13 +15,13 @@ impl ToSql for Value {
 
 /// Deserialize text/blob to JSON `Value`.
 impl FromSql for Value {
-    fn column_result(value: ValueRef) -> Result<Self> {
+    fn column_result(value: ValueRef) -> FromSqlResult<Self> {
         match value {
                 ValueRef::Text(ref s) => serde_json::from_str(s),
                 ValueRef::Blob(ref b) => serde_json::from_slice(b),
-                _ => return Err(Error::InvalidColumnType),
+                _ => return Err(FromSqlError::InvalidType),
             }
-            .map_err(|err| Error::FromSqlConversionFailure(Box::new(err)))
+            .map_err(|err| FromSqlError::Other(Box::new(err)))
     }
 }
 

src/types/time.rs

@@ -1,7 +1,7 @@
 extern crate time;
 
-use {Error, Result};
+use Result;
-use types::{FromSql, ToSql, ToSqlOutput, ValueRef};
+use types::{FromSql, FromSqlError, FromSqlResult, ToSql, ToSqlOutput, ValueRef};
 
 const SQLITE_DATETIME_FMT: &'static str = "%Y-%m-%d %H:%M:%S";
 
@@ -13,10 +13,10 @@ impl ToSql for time::Timespec {
 }
 
 impl FromSql for time::Timespec {
-    fn column_result(value: ValueRef) -> Result<Self> {
+    fn column_result(value: ValueRef) -> FromSqlResult<Self> {
         value.as_str().and_then(|s| match time::strptime(s, SQLITE_DATETIME_FMT) {
             Ok(tm) => Ok(tm.to_timespec()),
-            Err(err) => Err(Error::FromSqlConversionFailure(Box::new(err))),
+            Err(err) => Err(FromSqlError::Other(Box::new(err))),
         })
     }
 }

src/types/value.rs

@@ -1,4 +1,4 @@
-use super::Null;
+use super::{Null, Type};
 
 /// Owning [dynamic type value](http://sqlite.org/datatype3.html). Value's type is typically
 /// dictated by SQLite (not by the caller).
@@ -59,3 +59,15 @@ impl From<Vec<u8>> for Value {
         Value::Blob(v)
     }
 }
+
+impl Value {
+    pub fn data_type(&self) -> Type {
+        match *self {
+            Value::Null => Type::Null,
+            Value::Integer(_) => Type::Integer,
+            Value::Real(_) => Type::Real,
+            Value::Text(_) => Type::Text,
+            Value::Blob(_) => Type::Blob,
+        }
+    }
+}

src/types/value_ref.rs

@@ -1,6 +1,5 @@
-use ::Result;
+use ::types::{FromSqlError, FromSqlResult};
-use ::error::Error;
+use super::{Value, Type};
-use super::Value;
 
 /// A non-owning [dynamic type value](http://sqlite.org/datatype3.html). Typically the
 /// memory backing this value is owned by SQLite.
@@ -20,40 +19,52 @@ pub enum ValueRef<'a> {
     Blob(&'a [u8]),
 }
 
+impl<'a> ValueRef<'a> {
+    pub fn data_type(&self) -> Type {
+        match *self {
+            ValueRef::Null => Type::Null,
+            ValueRef::Integer(_) => Type::Integer,
+            ValueRef::Real(_) => Type::Real,
+            ValueRef::Text(_) => Type::Text,
+            ValueRef::Blob(_) => Type::Blob,
+        }
+    }
+}
+
 impl<'a> ValueRef<'a> {
     /// If `self` is case `Integer`, returns the integral value. Otherwise, returns
     /// `Err(Error::InvalidColumnType)`.
-    pub fn as_i64(&self) -> Result<i64> {
+    pub fn as_i64(&self) -> FromSqlResult<i64> {
         match *self {
             ValueRef::Integer(i) => Ok(i),
-            _ => Err(Error::InvalidColumnType),
+            _ => Err(FromSqlError::InvalidType),
         }
     }
 
     /// If `self` is case `Real`, returns the floating point value. Otherwise, returns
     /// `Err(Error::InvalidColumnType)`.
-    pub fn as_f64(&self) -> Result<f64> {
+    pub fn as_f64(&self) -> FromSqlResult<f64> {
         match *self {
             ValueRef::Real(f) => Ok(f),
-            _ => Err(Error::InvalidColumnType),
+            _ => Err(FromSqlError::InvalidType),
         }
     }
 
     /// If `self` is case `Text`, returns the string value. Otherwise, returns
     /// `Err(Error::InvalidColumnType)`.
-    pub fn as_str(&self) -> Result<&str> {
+    pub fn as_str(&self) -> FromSqlResult<&str> {
         match *self {
             ValueRef::Text(ref t) => Ok(t),
-            _ => Err(Error::InvalidColumnType),
+            _ => Err(FromSqlError::InvalidType),
         }
     }
 
     /// If `self` is case `Blob`, returns the byte slice. Otherwise, returns
     /// `Err(Error::InvalidColumnType)`.
-    pub fn as_blob(&self) -> Result<&[u8]> {
+    pub fn as_blob(&self) -> FromSqlResult<&[u8]> {
         match *self {
             ValueRef::Blob(ref b) => Ok(b),
-            _ => Err(Error::InvalidColumnType),
+            _ => Err(FromSqlError::InvalidType),
         }
     }
 }