statements: expose API to unset (serial) consistency

This is required by the CPP Rust Driver, and also useful for Rust Driver
direct users. See #1384 for details.

Author: wprzytula

scylla/src/statement/batch.rs

@@ -67,6 +67,13 @@ impl Batch {
         self.config.consistency = Some(c);
     }
 
+    /// Unsets the consistency overridden on this batch.
+    /// This means that consistency will be derived from the execution profile
+    /// (per-batch or, if absent, the default one).
+    pub fn unset_consistency(&mut self) {
+        self.config.consistency = None;
+    }
+
     /// Gets the consistency to be used when executing this batch if it is filled.
     /// If this is empty, the default_consistency of the session will be used.
     pub fn get_consistency(&self) -> Option<Consistency> {
@@ -79,6 +86,13 @@ impl Batch {
         self.config.serial_consistency = Some(sc);
     }
 
+    /// Unsets the serial consistency overridden on this batch.
+    /// This means that serial consistency will be derived from the execution profile
+    /// (per-batch or, if absent, the default one).
+    pub fn unset_serial_consistency(&mut self) {
+        self.config.serial_consistency = None;
+    }
+
     /// Gets the serial consistency to be used when executing this batch.
     /// (Ignored unless the batch is an LWT)
     pub fn get_serial_consistency(&self) -> Option<SerialConsistency> {

scylla/src/statement/prepared.rs

@@ -298,6 +298,13 @@ impl PreparedStatement {
         self.config.consistency = Some(c);
     }
 
+    /// Unsets the consistency overridden on this statement.
+    /// This means that consistency will be derived from the execution profile
+    /// (per-statement or, if absent, the default one).
+    pub fn unset_consistency(&mut self) {
+        self.config.consistency = None;
+    }
+
     /// Gets the consistency to be used when executing this prepared statement if it is filled.
     /// If this is empty, the default_consistency of the session will be used.
     pub fn get_consistency(&self) -> Option<Consistency> {
@@ -310,6 +317,13 @@ impl PreparedStatement {
         self.config.serial_consistency = Some(sc);
     }
 
+    /// Unsets the serial consistency overridden on this statement.
+    /// This means that serial consistency will be derived from the execution profile
+    /// (per-statement or, if absent, the default one).
+    pub fn unset_serial_consistency(&mut self) {
+        self.config.serial_consistency = None;
+    }
+
     /// Gets the serial consistency to be used when executing this statement.
     /// (Ignored unless the statement is an LWT)
     pub fn get_serial_consistency(&self) -> Option<SerialConsistency> {

scylla/src/statement/unprepared.rs

@@ -60,6 +60,13 @@ impl Statement {
         self.config.consistency = Some(c);
     }
 
+    /// Unsets the consistency overridden on this statement.
+    /// This means that consistency will be derived from the execution profile
+    /// (per-statement or, if absent, the default one).
+    pub fn unset_consistency(&mut self) {
+        self.config.consistency = None;
+    }
+
     /// Gets the consistency to be used when executing this statement if it is filled.
     /// If this is empty, the default_consistency of the session will be used.
     pub fn get_consistency(&self) -> Option<Consistency> {
@@ -72,6 +79,13 @@ impl Statement {
         self.config.serial_consistency = Some(sc);
     }
 
+    /// Unsets the serial consistency overridden on this statement.
+    /// This means that serial consistency will be derived from the execution profile
+    /// (per-statement or, if absent, the default one).
+    pub fn unset_serial_consistency(&mut self) {
+        self.config.serial_consistency = None;
+    }
+
     /// Gets the serial consistency to be used when executing this statement.
     /// (Ignored unless the statement is an LWT)
     pub fn get_serial_consistency(&self) -> Option<SerialConsistency> {