diesel 1.4.2

A safe, extensible ORM and Query Builder for PostgreSQL, SQLite, and MySQL
Documentation 
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131

use backend::UsesAnsiSavepointSyntax;
use connection::{Connection, SimpleConnection};
use result::QueryResult;

/// Manages the internal transaction state for a connection.
///
/// You will not need to interact with this trait, unless you are writing an
/// implementation of [`Connection`](trait.Connection.html).
pub trait TransactionManager<Conn: Connection> {
    /// Begin a new transaction or savepoint
    ///
    /// If the transaction depth is greater than 0,
    /// this should create a savepoint instead.
    /// This function is expected to increment the transaction depth by 1.
    fn begin_transaction(&self, conn: &Conn) -> QueryResult<()>;

    /// Rollback the inner-most transaction or savepoint
    ///
    /// If the transaction depth is greater than 1,
    /// this should rollback to the most recent savepoint.
    /// This function is expected to decrement the transaction depth by 1.
    fn rollback_transaction(&self, conn: &Conn) -> QueryResult<()>;

    /// Commit the inner-most transaction or savepoint
    ///
    /// If the transaction depth is greater than 1,
    /// this should release the most recent savepoint.
    /// This function is expected to decrement the transaction depth by 1.
    fn commit_transaction(&self, conn: &Conn) -> QueryResult<()>;

    /// Fetch the current transaction depth
    ///
    /// Used to ensure that `begin_test_transaction` is not called when already
    /// inside of a transaction.
    fn get_transaction_depth(&self) -> u32;
}

use std::cell::Cell;

/// An implementation of `TransactionManager` which can be used for backends
/// which use ANSI standard syntax for savepoints such as SQLite and PostgreSQL.
#[allow(missing_debug_implementations)]
#[derive(Default)]
pub struct AnsiTransactionManager {
    transaction_depth: Cell<i32>,
}

impl AnsiTransactionManager {
    /// Create a new transaction manager
    pub fn new() -> Self {
        AnsiTransactionManager::default()
    }

    fn change_transaction_depth(&self, by: i32, query: QueryResult<()>) -> QueryResult<()> {
        if query.is_ok() {
            self.transaction_depth
                .set(self.transaction_depth.get() + by)
        }
        query
    }

    /// Begin a transaction with custom SQL
    ///
    /// This is used by connections to implement more complex transaction APIs
    /// to set things such as isolation levels.
    /// Returns an error if already inside of a transaction.
    pub fn begin_transaction_sql<Conn>(&self, conn: &Conn, sql: &str) -> QueryResult<()>
    where
        Conn: SimpleConnection,
    {
        use result::Error::AlreadyInTransaction;

        if self.transaction_depth.get() == 0 {
            self.change_transaction_depth(1, conn.batch_execute(sql))
        } else {
            Err(AlreadyInTransaction)
        }
    }
}

impl<Conn> TransactionManager<Conn> for AnsiTransactionManager
where
    Conn: Connection,
    Conn::Backend: UsesAnsiSavepointSyntax,
{
    fn begin_transaction(&self, conn: &Conn) -> QueryResult<()> {
        let transaction_depth = self.transaction_depth.get();
        self.change_transaction_depth(
            1,
            if transaction_depth == 0 {
                conn.batch_execute("BEGIN")
            } else {
                conn.batch_execute(&format!("SAVEPOINT diesel_savepoint_{}", transaction_depth))
            },
        )
    }

    fn rollback_transaction(&self, conn: &Conn) -> QueryResult<()> {
        let transaction_depth = self.transaction_depth.get();
        self.change_transaction_depth(
            -1,
            if transaction_depth == 1 {
                conn.batch_execute("ROLLBACK")
            } else {
                conn.batch_execute(&format!(
                    "ROLLBACK TO SAVEPOINT diesel_savepoint_{}",
                    transaction_depth - 1
                ))
            },
        )
    }

    fn commit_transaction(&self, conn: &Conn) -> QueryResult<()> {
        let transaction_depth = self.transaction_depth.get();
        self.change_transaction_depth(
            -1,
            if transaction_depth <= 1 {
                conn.batch_execute("COMMIT")
            } else {
                conn.batch_execute(&format!(
                    "RELEASE SAVEPOINT diesel_savepoint_{}",
                    transaction_depth - 1
                ))
            },
        )
    }

    fn get_transaction_depth(&self) -> u32 {
        self.transaction_depth.get() as u32
    }
}