com.github.explainable.sql.table.BaseTable.java Source code

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Here is the source code for com.github.explainable.sql.table.BaseTable.java

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/*
 * The MIT License (MIT)
 *
 * Copyright (c) 2014 Gabriel Bender
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in all
 * copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */

package com.github.explainable.sql.table;

import com.github.explainable.sql.constraint.EqualityConstraint;
import com.github.explainable.sql.type.PrimitiveType;
import com.github.explainable.util.LDVertex;
import com.google.common.base.Preconditions;
import com.google.common.collect.ImmutableList;

import javax.annotation.Nonnull;
import javax.annotation.Nullable;

/**
 * Class that represents a single instance of a base table (i.e., a table that is stored by the DBMS
 * and is visible in the database schema.) Two instances of the same table can appear in the same
 * query; in this case, we will define two separate base tables. This will happen, e.g., for the
 * query {@code SELECT * FROM Table AS T1, Table AS T2}. If two columns reference the same table
 * instance, as in {@code SELECT X, Y FROM Table}, then only one BaseTable object will be created.
 */
public final class BaseTable extends Table {
    private final TypedRelation relation;

    private final String alias;

    private final NestedScope scope;

    // Lazily initialized the first time it's used; should only be accessed through columns().
    @Nullable
    private ImmutableList<BaseColumn> columns;

    @Nullable
    private LDVertex<Object, EqualityConstraint> conditionVertex;

    /**
     * Internally, there's a cyclic dependency between {@link BaseTable} and {@link BaseColumn}: every
     * {@link BaseTable} has a list of child columns, and every {@link BaseColumn} has a parent, which
     * is a {@link BaseTable}. We get around the dependency while making both classes effectively
     * immutable by using a private constructor and initializing the {@link #columns} attribute in a
     * static factory method.
     */
    private BaseTable(TypedRelation relation, String alias, NestedScope scope) {
        this.relation = Preconditions.checkNotNull(relation);
        this.alias = Preconditions.checkNotNull(alias);
        this.scope = Preconditions.checkNotNull(scope);

        // Postpone initializing the columns in order to avoid creating a cyclic dependency between
        // the constructors of BaseTable and {@link BaseColumn}.
        this.columns = null;

        this.conditionVertex = null;
    }

    /**
     * Create a new {@link BaseTable} with the specified relation and alias. It no alias is specified
     * then this method will default to using the relation name as an alias.
     */
    public static BaseTable create(TypedRelation relation, String alias, NestedScope scope) {
        return new BaseTable(relation, alias, scope);
    }

    @Nonnull
    @Override
    public ImmutableList<BaseColumn> columns() {
        if (columns == null) {
            ImmutableList<String> fieldNames = relation.columnNames();
            ImmutableList<PrimitiveType> types = relation.type().columnTypes();

            ImmutableList.Builder<BaseColumn> columnsBuilder = ImmutableList.builder();
            for (int i = 0; i < fieldNames.size(); i++) {
                columnsBuilder.add(new BaseColumn(fieldNames.get(i), this, types.get(i)));
            }

            columns = columnsBuilder.build();
        }

        return columns;
    }

    @Override
    public String alias() {
        return alias;
    }

    public NestedScope scope() {
        return scope;
    }

    public TypedRelation relation() {
        return relation;
    }

    public LDVertex<Object, EqualityConstraint> getConditionVertex() {
        Preconditions.checkState(conditionVertex != null);
        return conditionVertex;
    }

    public void setConditionVertex(LDVertex<Object, EqualityConstraint> vertex) {
        conditionVertex = Preconditions.checkNotNull(vertex);
    }

    @Override
    public String toString() {
        return "BaseTable(" + relation + ")";
    }
}