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package edu.caltech.nanodb.expressions;
import java.util.ArrayList;
import java.util.Collection;
import java.util.HashSet;
import java.util.Iterator;
import java.util.List;
import edu.caltech.nanodb.relations.ColumnInfo;
import edu.caltech.nanodb.relations.ColumnType;
import edu.caltech.nanodb.relations.Schema;
import edu.caltech.nanodb.relations.SchemaNameException;
/**
* This class provides the standard Boolean logical operators AND, OR, and NOT,
* for two or more terms (or exactly one term, in the case of NOT). In
* addition, there are several methods provided for manipulating Boolean
* expressions, since many plan equivalence-rules involve manipulations of the
* Boolean logical expressions associated with Select and Theta-Join plan nodes.
*/
public class BooleanOperator extends Expression {
/**
* This enumeration specifies the different kinds of Boolean operators that
* this class can implement.
*/
public enum Type {
AND_EXPR("AND"),
OR_EXPR("OR"),
NOT_EXPR("NOT");
/** The string representation for each operator. Used for printing. **/
private final String stringRep;
/**
* Construct a Type enum with the specified string representation.
*
* @param rep the string representation of the type
*/
Type(String rep) {
stringRep = rep;
}
/**
* Accessor for the operator type's string representation.
*
* @return the string representation of the operator type
*/
public String stringRep() {
return stringRep;
}
}
/** Specifies the type of this Boolean operator. */
private Type type;
/**
* The list of one or more terms in this expression. If the expression type
* is {@link BooleanOperator.Type#NOT_EXPR} then this will contain exactly
* one term.
*/
private ArrayList<Expression> terms;
public BooleanOperator(Type type, Collection<Expression> terms) {
if (type == null)
throw new NullPointerException("type cannot be null");
this.type = type;
this.terms = new ArrayList<Expression>();
if (terms != null) {
for (Expression term : terms)
addTerm(term);
}
}
public BooleanOperator(Type type) {
this(type, null);
}
/**
* Returns the type of this Boolean expression.
*
* @return the type of this Boolean expression.
*/
public Type getType() {
return type;
}
public void addTerm(Expression term) {
if (term == null)
throw new NullPointerException("term cannot be null");
terms.add(term);
}
public Expression getTerm(int i) {
return terms.get(i);
}
public ColumnInfo getColumnInfo(Schema schema) throws SchemaNameException {
// Boolean operators always return Boolean values, so just pass a
// Boolean value in to the TypeConverter to get out the corresponding
// SQL datatype.
ColumnType colType =
new ColumnType(TypeConverter.getSQLType(Boolean.FALSE));
return new ColumnInfo(colType);
}
public Object evaluate(Environment env) throws ExpressionException {
if (terms.size() == 0) {
throw new ExpressionException("Boolean " + type +
" expression contains no terms!");
}
Object objResult;
boolean boolResult;
if (type == Type.NOT_EXPR) {
if (terms.size() != 1) {
throw new ExpressionException(
"NOT-expressions may have only one term.");
}
// Evaluate the term...
objResult = terms.get(0).evaluate(env);
if (objResult == null)
boolResult = false; // TODO: this is UNKNOWN, not FALSE.
else
boolResult = TypeConverter.getBooleanValue(objResult);
// ...then negate it.
boolResult = !boolResult;
}
else {
// AND/OR expression.
if (terms.size() < 1) {
throw new ExpressionException(type.stringRep() +
"-expressions must have at least one term.");
}
if (type == Type.AND_EXPR) {
boolResult = true;
}
else {
assert type == Type.OR_EXPR : "Unexpected type value " + type + "!";
boolResult = false;
}
for (Expression term : terms) {
// Evaluate the i-th term, and combine it with the current answer.
objResult = term.evaluate(env);
boolean termValue;
if (objResult == null)
termValue = false; // TODO: this is UNKNOWN, not FALSE.
else
termValue = TypeConverter.getBooleanValue(objResult);
if (type == Type.AND_EXPR && !termValue) {
// AND term is false, so we are done. Answer is false.
boolResult = false;
break;
}
else if (type == Type.OR_EXPR && termValue) {
// OR term is true, so we are done. Answer is true.
boolResult = true;
break;
}
}
}
return Boolean.valueOf(boolResult);
}
@Override
public Expression traverse(ExpressionProcessor p) {
p.enter(this);
for (int i = 0; i < terms.size(); i++) {
Expression e = terms.get(i).traverse(p);
terms.set(i, e);
}
return p.leave(this);
}
/**
* Returns a string representation of this Boolean logical expression and
* its subexpressions, including parentheses where necessary to specify
* precedence.
*/
@Override
public String toString() {
// Convert all of the components into string representations.
StringBuilder buf = new StringBuilder();
if (type == Type.NOT_EXPR) {
assert terms.size() == 1 : "NOT expressions must have exactly one term";
buf.append(type.stringRep());
buf.append(' ');
Expression term = terms.get(0);
String termStr = term.toString();
if (term instanceof BooleanOperator) {
BooleanOperator termOp = (BooleanOperator) term;
if (termOp.type != Type.NOT_EXPR)
termStr = '(' + termStr + ')';
}
buf.append(termStr);
}
else if (type == Type.AND_EXPR) {
assert terms.size() >= 1 : "AND expressions must have at least one term";
boolean first = true;
for (Expression term : terms) {
if (first)
first = false;
else
buf.append(' ').append(type.stringRep()).append(' ');
String termStr = term.toString();
if (term instanceof BooleanOperator) {
BooleanOperator termOp = (BooleanOperator) term;
if (termOp.type == Type.OR_EXPR)
termStr = '(' + termStr + ')';
}
buf.append(termStr);
}
}
else { // OR_EXPR
assert type == Type.OR_EXPR;
assert terms.size() >= 1 : "OR expressions must have at least one term";
boolean first = true;
for (Expression term : terms) {
if (first)
first = false;
else
buf.append(' ').append(type.stringRep()).append(' ');
buf.append(term.toString());
}
}
return buf.toString();
}
/**
* This method returns true if this Boolean expression contains any terms
* that reference the exact set of tables specified in the arguments. See
* the documentation for {@link #getTermsReferencingAllTables} for more
* details on what is considered to be a "matching" term by this method.
*
* @design This method is <em>slightly</em> more efficient than the
* get/remove methods, since it stops after it has found the first
* term that satisfies the specified conditions. However, if there
* will be a subsequent call to the get or remove method, it's
* probably most efficient to just call it directly.
*
* @param tableNames a collection of table-names to look for in the terms.
*
* @return A list of terms that reference all of the tables specified in the
* input list, and no others.
*/
public boolean hasTermsReferencingAllTables(String... tableNames) {
// Put table names into a set so we can easily do membership tests.
HashSet<String> inputTables = new HashSet<String>();
for (String tableName : tableNames)
inputTables.add(tableName);
// Iterate through each term in this Boolean operator. For each term,
// find out what symbols the term contains. Then, see if the term only
// references the tables in the input set.
HashSet<ColumnName> symbols = new HashSet<ColumnName>();
HashSet<String> exprTables = new HashSet<String>();
for (Expression term : terms) {
symbols.clear();
exprTables.clear();
term.getAllSymbols(symbols);
for (ColumnName colName : symbols) {
if (colName.isTableSpecified())
exprTables.add(colName.getTableName());
}
if (inputTables.equals(exprTables))
return true;
}
return false;
}
/**
* This method finds and returns a list of all terms in this Boolean
* expression that reference the exact set of tables specified in the
* arguments. If a term references other tables outside of this set then it
* will not be returned. If a term doesn't reference some table in this set
* then it will not be returned.
*
* @param tableNames a collection of table-names to look for in the terms.
*
* @return A list of terms that reference all of the tables specified in the
* input list, and no others.
*/
public List<Expression> getTermsReferencingAllTables(String... tableNames) {
// Call the helper, with "remove" flag set to false.
return _getTermsReferencingAllTables(tableNames, false);
}
/**
* This method finds, removes, and returns a list of all terms in this
* Boolean expression that reference the exact set of tables specified in
* the arguments. If a term references other tables outside of this set
* then it will not be returned. If a term doesn't reference some table in
* this set then it will not be returned.
* <p>
* The sole difference between this and {@link #getTermsReferencingAllTables}
* is that this method also removes the found terms from this Boolean
* expression object.
*
* @param tableNames a collection of table-names to look for in the terms.
*
* @return A list of terms that reference all of the tables specified in the
* input list, and no others. These terms are also removed from the
* Boolean expression object.
*/
public List<Expression> removeTermsReferencingAllTables(String... tableNames) {
// Call the helper, with "remove" flag set to true.
return _getTermsReferencingAllTables(tableNames, true);
}
/**
* This is a private helper function used by both the
* {@link #getTermsReferencingAllTables} and
* {@link #removeTermsReferencingAllTables} methods.
*
* @param tableNames an array of table-names to look for in the terms.
* @param remove if <tt>true</tt> then matching terms will be removed from
* this Boolean operator's list of terms.
*
* @return A list of terms that reference all of the tables specified in the
* input list, and no others.
*/
private List<Expression> _getTermsReferencingAllTables(String[] tableNames,
boolean remove) {
ArrayList<Expression> found = new ArrayList<>();
// Put table names into a set so we can easily do membership tests.
HashSet<String> inputTables = new HashSet<>();
for (String tableName : tableNames)
inputTables.add(tableName);
// Iterate through each term in this Boolean operator. For each term,
// find out what symbols the term contains. Then, see if the term only
// references the tables in the input set.
HashSet<ColumnName> symbols = new HashSet<>();
HashSet<String> exprTables = new HashSet<>();
Iterator<Expression> termIter = terms.iterator();
while (termIter.hasNext()) {
Expression term = termIter.next();
symbols.clear();
exprTables.clear();
term.getAllSymbols(symbols);
for (ColumnName colName : symbols) {
if (colName.isTableSpecified())
exprTables.add(colName.getTableName());
}
if (inputTables.equals(exprTables)) {
found.add(term);
if (remove)
termIter.remove();
}
}
return found;
}
/**
* Returns the number of terms in the boolean expression.
*
* @return the number of terms in the boolean expression.
*/
public int getNumTerms() {
return terms.size();
}
/**
* Removes the i<sup>th</sup> term, starting from 0.
*
* @param i the index of the term to remove.
*
* @throws IllegalArgumentException if the specified index is invalid.
*/
public void removeTerm(int i) {
if (i < 0 || i >= getNumTerms()) {
throw new IllegalArgumentException("Term-index " + i +
" is out of range [0, " + getNumTerms() + ")");
}
terms.remove(i);
}
/**
* Simplifies a Boolean expression by eliminating and de-nesting as much of
* the expression as possible.
*/
@Override
public Expression simplify() {
// Go through and try to simplify anything we can inside the operator
for (int i = 0; i < terms.size(); i++) {
Expression e = terms.get(i);
terms.set(i, e.simplify());
}
// There is only one simplification for the NOT expression:
// NOT (NOT P) = P
if (type == Type.NOT_EXPR) {
assert terms.size() == 1;
if (terms.get(0) instanceof BooleanOperator) {
BooleanOperator nested = (BooleanOperator) terms.get(0);
if (nested.type == Type.NOT_EXPR) {
assert nested.terms.size() == 1;
return nested.terms.get(0);
}
}
// If we fall through to here, we can't do any simplification of
// the NOT expression.
return this;
}
// Handle AND and OR expression simplifications.
assert type == Type.AND_EXPR || type == Type.OR_EXPR;
// If there is only one term, just return the term.
if (terms.size() == 1)
return terms.get(0);
int i = 0;
while (i < terms.size()) {
Expression e = terms.get(i);
if (e instanceof BooleanOperator) {
BooleanOperator b = (BooleanOperator) e;
// If the nested Boolean operator is the same type as this
// one, we can lift up the terms and put them in this
// operator.
if (b.type == type) {
terms.remove(i);
terms.addAll(i, b.terms);
}
else {
i++;
}
// The way this loop is constructed, we will repeat this
// check/lift process for any child nodes we just lifted up,
// that are also BooleanOperators of the same type, since
// the new nodes will now be at index i.
}
}
return this;
}
/**
* Performs a value-eqality test for whether the specified object is an
* expression with the same structure and contents.
*
* @param obj the object to which we are comparing
*/
@Override
public boolean equals(Object obj) {
if (obj instanceof BooleanOperator) {
BooleanOperator other = (BooleanOperator) obj;
return (type == other.type && terms.equals(other.terms));
}
return false;
}
/**
* Computes the hash-code of an Expression.
*/
@Override
public int hashCode() {
int hash = 7;
hash = 31 * hash + type.hashCode();
hash = 31 * hash + terms.hashCode();
return hash;
}
/**
* Creates a copy of expression.
*/
@Override
@SuppressWarnings("unchecked")
protected Object clone() throws CloneNotSupportedException {
BooleanOperator expr = (BooleanOperator) super.clone();
// Type is immutable, copy it.
expr.type = this.type;
expr.terms = (ArrayList<Expression>) terms.clone();
return expr;
}
}