⚡️ Speed up method SQLDeleteCompiler._as_sql by 6%

[codeflash-ai]

📄 6% (0.06x) speedup for SQLDeleteCompiler._as_sql in django/db/models/sql/compiler.py

⏱️ Runtime : 19.2 microseconds → 18.1 microseconds (best of 115 runs)

📝 Explanation and details

The optimized code achieves a 6% speedup by reducing expensive attribute lookups and dictionary operations in the performance-critical quote_name_unless_alias method.

Key optimizations:

1. Local variable caching: The method now stores self.quote_cache, self.query, and query attributes (alias_map, table_map, etc.) in local variables. This eliminates repeated attribute lookups, which are costly in Python due to the attribute resolution mechanism.

2. Reduced dictionary lookups: The original code performed multiple query.external_aliases.get(name) calls in conditional expressions. The optimized version calls it once and stores the result in external_alias_value, avoiding redundant dictionary operations.

3. Streamlined conditional logic: The complex nested conditional in the original code was restructured to use explicit blocks, reducing the number of dictionary lookups and making the execution path more predictable.

4. Compiler method optimization: In the compile method, string concatenation is now done explicitly rather than within the getattr call, and vendor information is stored locally.

Performance benefits are most pronounced for:

• Basic delete operations (5-15% faster): The test results show consistent improvements across simple delete queries with where clauses
• Long table names (7.9% faster): Reduced attribute lookups help when processing longer identifiers
• Large-scale operations (2.9% faster): The caching benefits compound when processing many parameters

The optimization maintains identical functionality while targeting Python's performance characteristics around attribute access and dictionary operations.

✅ Correctness verification report:

Test	Status
⚙️ Existing Unit Tests	🔘 None Found
🌀 Generated Regression Tests	✅ 37 Passed
⏪ Replay Tests	🔘 None Found
🔎 Concolic Coverage Tests	🔘 None Found
📊 Tests Coverage	83.3%

🌀 Generated Regression Tests and Runtime

import pytest
from django.db.models.sql.compiler import SQLDeleteCompiler

# --- Minimal mock classes to support _as_sql function ---

class MockConnectionOps:
    """Mock of connection.ops with a quote_name method."""
    def quote_name(self, name):
        # Simulate quoting for SQL, e.g., wrap in double quotes
        return f'"{name}"'

class MockConnection:
    """Mock of a database connection."""
    vendor = "default"
    ops = MockConnectionOps()
    class features:
        supports_order_by_nulls_modifier = False
        order_by_nulls_first = False

class FullResultSet(Exception):
    """Mock exception for testing."""

class MockWhereNode:
    """Mock node for query.where."""
    def __init__(self, sql, params):
        self._sql = sql
        self._params = params
        self.as_sql_called = False

    def as_sql(self, compiler, connection):
        self.as_sql_called = True
        return self._sql, self._params

class MockQuery:
    """Mock query object for SQLDeleteCompiler."""
    def __init__(
        self,
        base_table,
        where=None,
        alias_map=None,
        table_map=None,
        extra_select=None,
        external_aliases=None,
        model=None,
    ):
        self.base_table = base_table
        self.where = where
        self.alias_map = alias_map or {}
        self.table_map = table_map or {}
        self.extra_select = extra_select or {}
        self.external_aliases = external_aliases or {}
        self.model = model or type("MockModel", (), {"__qualname__": "MockModel"})
from django.db.models.sql.compiler import SQLDeleteCompiler

# --- Unit tests ---

# 1. Basic Test Cases

def test_basic_delete_with_simple_where():
    """Test a standard delete with a simple where clause."""
    where = MockWhereNode("id = %s", [42])
    query = MockQuery(base_table="mytable", where=where)
    compiler = SQLDeleteCompiler(query, MockConnection(), "default")
    sql, params = compiler._as_sql(query) # 3.23μs -> 2.87μs (12.8% faster)

def test_basic_delete_with_multiple_params():
    """Test delete with a where clause having multiple parameters."""
    where = MockWhereNode("x = %s AND y = %s", [1, 2])
    query = MockQuery(base_table="tbl", where=where)
    compiler = SQLDeleteCompiler(query, MockConnection(), "default")
    sql, params = compiler._as_sql(query) # 2.44μs -> 2.32μs (5.17% faster)

def test_basic_delete_with_no_params():
    """Test delete with a where clause that has no parameters."""
    where = MockWhereNode("flag IS NULL", [])
    query = MockQuery(base_table="flags", where=where)
    compiler = SQLDeleteCompiler(query, MockConnection(), "default")
    sql, params = compiler._as_sql(query) # 2.22μs -> 2.18μs (1.88% faster)

# 2. Edge Test Cases


def test_delete_with_alias_in_quote_cache():
    """Test that quote_name_unless_alias uses cached value."""
    query = MockQuery(base_table="mytable")
    compiler = SQLDeleteCompiler(query, MockConnection(), "default")
    # Pre-populate the quote_cache
    compiler.quote_cache["mytable"] = "ALIAS"
    sql = compiler.quote_name_unless_alias("mytable")

def test_delete_with_alias_in_alias_map_not_table_map():
    """Test that alias in alias_map but not table_map is not quoted."""
    query = MockQuery(
        base_table="alias_table",
        alias_map={"alias_table": object()},
        table_map={},
    )
    compiler = SQLDeleteCompiler(query, MockConnection(), "default")
    quoted = compiler.quote_name_unless_alias("alias_table")

def test_delete_with_alias_in_extra_select():
    """Test that alias in extra_select is not quoted."""
    query = MockQuery(
        base_table="tbl",
        extra_select={"foo": object()},
    )
    compiler = SQLDeleteCompiler(query, MockConnection(), "default")
    quoted = compiler.quote_name_unless_alias("foo")

def test_delete_with_alias_in_external_aliases_not_table_map():
    """Test that alias in external_aliases and not in table_map is not quoted."""
    query = MockQuery(
        base_table="tbl",
        external_aliases={"bar": True},
        table_map={},
    )
    compiler = SQLDeleteCompiler(query, MockConnection(), "default")
    quoted = compiler.quote_name_unless_alias("bar")

def test_delete_with_alias_not_in_any_map():
    """Test that alias not in any map is quoted."""
    query = MockQuery(base_table="tbl")
    compiler = SQLDeleteCompiler(query, MockConnection(), "default")
    quoted = compiler.quote_name_unless_alias("baz")

def test_delete_with_star_table():
    """Test that '*' is always returned as '*'."""
    query = MockQuery(base_table="*")
    compiler = SQLDeleteCompiler(query, MockConnection(), "default")
    quoted = compiler.quote_name_unless_alias("*")

def test_delete_with_empty_where_sql():
    """Test delete with an empty where SQL (should still add WHERE)."""
    where = MockWhereNode("", [])
    query = MockQuery(base_table="tbl", where=where)
    compiler = SQLDeleteCompiler(query, MockConnection(), "default")
    sql, params = compiler._as_sql(query) # 2.98μs -> 2.59μs (14.9% faster)

def test_delete_with_non_string_base_table():
    """Test that non-string base_table is handled (should be quoted as str)."""
    where = MockWhereNode("id=1", [])
    query = MockQuery(base_table=123, where=where)
    compiler = SQLDeleteCompiler(query, MockConnection(), "default")
    sql, params = compiler._as_sql(query) # 2.72μs -> 2.75μs (1.16% slower)

# 3. Large Scale Test Cases

def test_delete_with_large_number_of_params():
    """Test delete with a large number of parameters."""
    N = 500
    where_sql = " AND ".join([f"col{i} = %s" for i in range(N)])
    params = list(range(N))
    where = MockWhereNode(where_sql, params)
    query = MockQuery(base_table="bigtable", where=where)
    compiler = SQLDeleteCompiler(query, MockConnection(), "default")
    sql, out_params = compiler._as_sql(query) # 3.24μs -> 3.15μs (2.86% faster)

def test_delete_with_long_table_name():
    """Test delete with a very long table name."""
    long_name = "t" * 255
    where = MockWhereNode("id=1", [])
    query = MockQuery(base_table=long_name, where=where)
    compiler = SQLDeleteCompiler(query, MockConnection(), "default")
    sql, params = compiler._as_sql(query) # 2.39μs -> 2.21μs (7.90% faster)

def test_delete_with_many_quote_name_calls():
    """Test that quote_name_unless_alias caches results for many names."""
    query = MockQuery(base_table="tbl")
    compiler = SQLDeleteCompiler(query, MockConnection(), "default")
    for i in range(100):
        name = f"col_{i}"
        quoted = compiler.quote_name_unless_alias(name)

def test_delete_with_many_aliases():
    """Test quote_name_unless_alias with many aliases in alias_map."""
    alias_map = {f"alias_{i}": object() for i in range(100)}
    query = MockQuery(base_table="tbl", alias_map=alias_map)
    compiler = SQLDeleteCompiler(query, MockConnection(), "default")
    for i in range(100):
        name = f"alias_{i}"
        quoted = compiler.quote_name_unless_alias(name)
# codeflash_output is used to check that the output of the original code is the same as that of the optimized code.
#------------------------------------------------
import pytest
from django.db.models.sql.compiler import SQLDeleteCompiler


# --- Function to test ---
# Minimal implementation of _as_sql for unit testing purposes.
# The function generates a DELETE SQL statement for a given query object.
def _as_sql(query):
    """
    Generate a DELETE SQL statement for the given query object.
    - query.base_table: str, the name of the table to delete from
    - query.where: an object with as_sql(compiler, connection) method, returning (sql, params)
    - query.connection: an object with ops.quote_name(name) method
    - query.quote_name_unless_alias(name): function to quote table names
    """
    # Emulate quote_name_unless_alias logic
    def quote_name_unless_alias(name):
        # For testing, just wrap the name in double quotes unless it's "*"
        if name == "*":
            return "*"
        return f'"{name}"'

    delete = "DELETE FROM %s" % quote_name_unless_alias(query.base_table)
    try:
        where, params = query.where.as_sql(query, query.connection)
    except Exception as e:
        # Simulate catching FullResultSet (which means return empty result)
        if isinstance(e, FullResultSet):
            return delete, ()
        raise
    return f"{delete} WHERE {where}", tuple(params)

# --- Helper classes for mocking ---
class FullResultSet(Exception):
    """Mock exception representing a full result set (no WHERE clause)."""

class DummyWhere:
    def __init__(self, sql, params):
        self.sql = sql
        self.params = params
    def as_sql(self, compiler, connection):
        return self.sql, self.params

class DummyConnection:
    class ops:
        @staticmethod
        def quote_name(name):
            # Simulate quoting a table name (for testing, wrap in double quotes)
            if name == "*":
                return "*"
            return f'"{name}"'

class DummyQuery:
    def __init__(self, base_table, where, connection=None):
        self.base_table = base_table
        self.where = where
        self.connection = connection or DummyConnection()

# --- Unit tests ---
# 1. Basic Test Cases

To edit these changes git checkout codeflash/optimize-SQLDeleteCompiler._as_sql-mh6iz71p and push.