sqlalchemy IS NOT NULL选择

Question

如何在SQL中添加过滤器以从某列中选择NOT NULL值？

SELECT * 
FROM table 
WHERE YourColumn IS NOT NULL;

如何使用SQLAlchemy过滤器执行相同的操作？

select = select(table).select_from(table).where(all_filters) 

Answer 1

column_obj != None将生成IS NOT NULL constraint：

  

在列上下文中，生成子句a != b。如果目标是None，则生成IS NOT NULL。

或使用isnot()（0.7.9中的新内容）：

  

实施IS NOT运营商。

     

通常，与IS NOT的值进行比较时会自动生成None，该值会解析为NULL。但是，如果与某些平台上的布尔值进行比较，则可能需要明确使用IS NOT。

演示：

>>> from sqlalchemy.sql import column
>>> column('YourColumn') != None
<sqlalchemy.sql.elements.BinaryExpression object at 0x10c8d8b90>
>>> str(column('YourColumn') != None)
'"YourColumn" IS NOT NULL'
>>> column('YourColumn').isnot(None)
<sqlalchemy.sql.elements.BinaryExpression object at 0x104603850>
>>> str(column('YourColumn').isnot(None))
'"YourColumn" IS NOT NULL'

Answer 2

从版本0.7.9开始，您可以使用过滤器运算符.isnot而不是比较约束，如下所示：

query.filter(User.name.isnot(None))

只有在关注pep8时才需要此方法。

来源：sqlalchemy documentation

Answer 3

如果其他人想知道，您可以使用 public class RegisterActivity extends AppCompatActivity { private FirebaseAuth mAuth; private FirebaseAuth.AuthStateListener mAuthListener; private EditText mUsernameField; private EditText mPasswordField; private EditText mConfirmPasswordField; private Button mRegisterButton; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_register); Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar); setSupportActionBar(toolbar); mUsernameField = (EditText) findViewById(R.id.enterUsername); mPasswordField = (EditText) findViewById(R.id.enterPassword); mConfirmPasswordField = (EditText) findViewById(R.id.confirmPassword); mRegisterButton = (Button) findViewById(R.id.confirmRegistration); mRegisterButton.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { createAccount(mUsernameField.getText().toString(), mPasswordField.getText().toString()); } }); mAuth = FirebaseAuth.getInstance(); mAuthListener = new FirebaseAuth.AuthStateListener() { @Override public void onAuthStateChanged(@NonNull FirebaseAuth firebaseAuth) { FirebaseUser user = firebaseAuth.getCurrentUser(); if (user != null) { // User is signed in Log.d("account", "onAuthStateChanged:signed_in:" + user.getUid()); } else { // User is signed out Log.d("account", "onAuthStateChanged:signed_out"); } // ... } }; } @Override public void onStart() { super.onStart(); mAuth.addAuthStateListener(mAuthListener); } @Override public void onStop() { super.onStop(); if (mAuthListener != null) { mAuth.removeAuthStateListener(mAuthListener); } } private void createAccount(String email, String password) { Log.d("account", "createAccount:" + email); if (!validateForm()) { return; } // [START create_user_with_email] mAuth.createUserWithEmailAndPassword(email, password) .addOnCompleteListener(this, new OnCompleteListener() { @Override public void onComplete(@NonNull Task task) { Log.d("account", "createUserWithEmail:onComplete:" + task.isSuccessful()); // If sign in fails, display a message to the user. If sign in succeeds // the auth state listener will be notified and logic to handle the // signed in user can be handled in the listener. if (!task.isSuccessful()) { Toast.makeText(RegisterActivity.this, R.string.register_failed, Toast.LENGTH_SHORT).show(); } else { Intent intent = new Intent(RegisterActivity.this, MainActivity.class); RegisterActivity.this.startActivity(intent); finish(); } } }); // [END create_user_with_email] } private boolean validateForm() { boolean valid = true; String email = mUsernameField.getText().toString(); if (TextUtils.isEmpty(email)) { mUsernameField.setError("Required."); valid = false; } else { mUsernameField.setError(null); } String password = mPasswordField.getText().toString(); if (TextUtils.isEmpty(password)) { mPasswordField.setError("Required."); valid = false; } else { mPasswordField.setError(null); } String confirmPassword = mConfirmPasswordField.getText().toString(); if (TextUtils.isEmpty(confirmPassword)) { mConfirmPasswordField.setError("Required."); valid = false; } else { mConfirmPasswordField.setError(null); } if(!confirmPassword.equals(password)) { mConfirmPasswordField.setError("Passwords must be the same."); valid = false; } return valid; } } 生成is_：

>>> from sqlalchemy.sql import column
>>> print column('foo').is_(None)
foo IS NULL
>>> print column('foo').isnot(None)
foo IS NOT NULL

Answer 4

对我来说，如果我执行以下操作，那么我将获得预期的行为：

query = query.filter(Model1.column1 == None)

如果我执行以下操作，则似乎未应用该过滤器：

query = query.filter(Model1.column1 is None)