用外鍵創建表

Question

我編寫了一個創建表的函數：

def createSQLCreateTableCommand(tableName, columns, foreignKeys):
    columns = ["%s"%(c) for c in columns]
    foreignKeys = ["FOREIGN KEY (%s) REFERENCES %s(%s)"%(fk[0],fk[1],fk[2]) for fk in foreignKeys]
    cmd = """CREATE TABLE IF NOT EXISTS %s (%s)"""%(tableName,','.join(columns+foreignKeys))
    return cmd

我想測試我的功能並編寫以下代碼。 “訪問”和“測試”只是帶有某些列的表。 在表“ test_result”中，它包含“訪問”表中的rowid的外鍵和“測試”表中的rowid的外鍵。 我的代碼適用於“訪問”和“測試”表，但無法演示“ test_result”表。 我不確定不能正確表達外鍵參數。 有人可以幫助我修復代碼嗎？

conn = sqlite.connect(":memory:")
cursor = conn.cursor()

sqlVisits = createSQLCreateTableCommand("visit",["visitid text"],[])
sqlTests = createSQLCreateTableCommand("test",["name text","unit text","low text","high text"],[])
sqlTestResults = createSQLCreateTableCommand("test_result",["value text","time_date text"],["visit int","test int"])    #this is not correct

cursor.execute(sqlVisits)
cursor.execute(sqlTests)
cursor.execute(sqlTestResults)
conn.commit()

cursor.execute("""SELECT tbl_name FROM sqlite_master WHERE type = 'table'""")
print cursor.fetchall()

Answer 1

當您打印函數的實際輸出時：

>>> createSQLCreateTableCommand("test_result",["value text","time_date text"],["visit int","test int"])
CREATE TABLE IF NOT EXISTS test_result (
    value text,
    time_date text,
    FOREIGN KEY (v) REFERENCES i(s),
    FOREIGN KEY (t) REFERENCES e(s)
)

您會看到類似fk[0]表達式從字符串中提取單個字符。

參數foreignKeys必須是一個由三個字符串組成的數組：子列名稱，父表名稱和父列名稱：

>>> print createSQLCreateTableCommand("test_result",
...                                   ["value text", "time_date text"],
...                                   [("visitid", "visit", "visitid"),
...                                    ("testname", "test", "name")])
CREATE TABLE IF NOT EXISTS test_result (
    value text,
    time_date text,
    FOREIGN KEY (visitid) REFERENCES visit(visitid),
    FOREIGN KEY (testname) REFERENCES test(name)
)

但是，這不是有效的SQL，因為FOREIGN KEY約束必須引用子表中的現有列。

要解決此問題，請更改createSQLCreateTableCommand函數以創建具有外鍵列約束的列：

>>> def createSQLCreateTableCommand(tableName, columns, foreignKeys):
...     columns = ["%s"%(c) for c in columns]
...     foreignKeys = ["%s REFERENCES %s(%s)"%(fk[0],fk[1],fk[2]) for fk in foreignKeys]
...     cmd = """CREATE TABLE IF NOT EXISTS %s (%s)"""%(tableName,','.join(columns+foreignKeys))
...     return cmd
...
>>> print createSQLCreateTableCommand("test_result",
...                                   ["value text", "time_date text"],
...                                   [("visitid text", "visit", "visitid"),
...                                    ("testname text", "test", "name")])
CREATE TABLE IF NOT EXISTS test_result (
    value text,
    time_date text,
    visitid text REFERENCES visit(visitid),
    testname text REFERENCES test(name)
)